AbstractThe hot deformation characteristics of Inconel 625 alloy were investigated by torsion testing at constant strain rates in the range of 0·17–5·3 s−1, and testing temperatures in the range of 950–1150°C. Examination of the microstructures was carried out by optical microscopy. The flow stress in the torsion test showed a single peak in the flow stress–strain curves and indicated that dynamic recrystallisation took place during hot torsion. The strain to the peak stress increased with decreasing temperature and increasing strain rate. Analysis of flow stress data at the peak gave an activation energy for deformation of 400 kJ mol−1. The relationship between peak stress, temperature, and strain rate can be expressed by the usual potential equation between the stress and the Zener–Hollomon parameter Z=εexp(Q/RT). Flow stress data obtained in the present work compare well with data published for similar superalloys. Fully dynamically recrystallised microstructures are observed at high temperatures and the dynamically recrystallised grain sizes drexare related to the flow stressσ. The actual results of the present work together with those found in the literature can be fitted to a relationship (σ∞drex−0·75). A range of temperature (between 1050 and 1100°C) in which ductility was maximised, and above which ductility decreased, was observed.MST/3357