Hot deformation characteristics of Inconel* 625

The 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 degrees C. Examination of the microstructures was carried out by optical microscopy. The flow stress in the torsion test skewed 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 = epsilon exp(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 d(rex) are related to the flow stress sigma. The actual results of the present work together with those found in the literature can befitted to a relationship (sigma proportional to d(rex)(0.75)). A range of temperature (between 1050 and 1100 degrees C) in which ductility was maximised and above which ductility decreased, was observed. (C) 1996 The Institute of Materials.