Effect of initial state on hot deformation and dynamic recrystallization of Ni-Fe based alloy GH984G for steam boiler applications

The effect of initial alloy state on hot deformation and dynamic recrystallization (DRX) of GH984G alloy, used to manufacture large scale forgings for 700 degrees C advanced ultra-supercritical (A-USC) coal-fired power plants, was studied by isothermal compression test. The experimental results show that the apparent activation energy of hot deformation for the as-cast alloy is larger than that of the hot-rolled alloy. The reasonable ranges of processing parameters for the as-cast and hot-rolled alloys are 1100-1200 degrees C/0.01 -0.5 s(-1) and 1100-1200 degrees C/1.0-10 s(-1), respectively, based on the processing maps. The flow instability domain of the as-cast alloy is larger than that of the hot-rolled alloy. The different hot deformation behaviors of the as-cast and hot-rolled alloys result from the various initial grain sizes and DRX mechanisms. The main DRX nucleation mode of the as-cast alloy with large grains is continuous dynamic recrystallization (CDRX). However, for the hot-rolled alloy with fine grains, the discontinuous dynamic recrystallization (DDRX) is dominant. (C) 2019 Elsevier B.V. All rights reserved.