20th International Forgemasters Meeting - IFM 2017

A digital engineering system using finite element (FE) analysis was developed in order to optimized forging and rolling process for obtaining an adequate microstructure in large-scale forged and rolled products. For precise prediction of changes in microstructure during forging and rolling, the re-crystallization behavior should be investigate carefully. Ni-based super alloys are usually required fine grain microstructure in order to enhance high performance mechanical properties at high temperature. So it is very important to control the microstructure in forging, rolling and heat treatment process. In conventional studies, there were some procedures of forming a fine grain microstructure. For example, they are promotion of dynamic re-crystallization with high plastic strain at super-solvus temperature and keeping grain growth with pining effect of delta phase at sub-solvus temperature in case of Alloy 718. Then new studies about re-crystallization behavior with coarse gamma prime are reported. However, there are a little reports about it right now. In this study, the re-crystallization behavior of a new Ni-based super alloy with coarse gamma prime at sub-solvus temperature was investigated experimentally. Investigation of re-crystallization rate and grain growth behavior was carried out by a Rastegaev compression test. Figure 1 shows microstructures of austenite grain, gamma prime and crystallographic orientation distribution (KAM value using EBSD). It was confirmed that the coarse gamma prime was remained at low temperature forging, and the static re-crystallization increasing new fine grain was promoted after heat treatment. As the result of analysis of KAM value by using EBSD, the low crystallographic orientation distribution was remained in old austenite grain without recovery. It was indicated that the phenomenon had a relationship to promotion of static re-crystallization.