Hot forging of a nickel-base superalloy

Compression tests were carried out to investigate the hot-deformation behav ior of nickel-based Alloy 718. The tests were conducted in the temperature range 982-1066 degreesC and the strain rate range 5 x 10(-4)-5.0 s(-1). Pan cakes were also made by multi-step forging and their microstructures were c ompared with specimen-base compression tests. Hot-deformation behavior was led mainly by dynamic recrystallization as wel l as by dynamic recovery. Dynamic recrystallization as well as meta-dynamic recrystallization plays a significant role in determining final microstruc tures for the given temperature ranges. Once the dynamic recrystallization is finished, no significant stress relaxation attributed to meta-dynamic re crystallization occurs and stress hardening following the intermittent dwel l time between the first and the second compression tests occurs even at 10 66 degreesC due to the fact that grain growth becomes prominent. In such two-step compression tests, large second strains produce second dyn amic recrystallization, which leads to fine grain sizes. To control the gra in size through dynamic recrystallization in multi-step forging, one needs to consider the strain partitioning in each forging step for the given temp erature and strain rate ranges. FEM simulation was used to evaluate the mic rostructural variation during pancake forging, taking into account the vari ation of grain sizes following dynamic recrystallization. (C) 2001 Elsevier Science B.V. All rights reserved.