Modeling of grain size in superalloy IN718 during hot deformation

The microstructure and mechanical properties of IN718 forgings are highly s ensitive to metallurgical technology and thermomechanical processing. To ob tain the most favorable mechanical properties and microstructures in IN718 forgings, it is necessary to further understand the microstructure variatio n behavior and to be able to predict the grain size of superalloy IN718 dur ing hot deformation. On the basis of isothermal constant-speed compression tests conducted using a computer-controlled MTS machine at temperatures fro m 960-1040 degrees C, with initial strain rates from 0.001-1.0 s(-1), to en gineering strains from 0.1-0.7, the microstructure variation behavior of su peralloy IN718 has been studied. Two different types of microstructures wer e found at deformation temperatures below and above 1000 degrees C. The eff ect of hot-deformation parameters on the microstructures was analyzed and a model was developed to describe the duplex microstructure and to express t he relationship between the grain size and the hot-deformation parameters. (C) 1999 Elsevier Science S.A. All rights reserved.