| Title |
Effects of Thermomechanical Treatments on the Microstructure and Mechanical Properties of Superalloy 718 |
| Authors |
최병학(Byung Hak Choe); 안형준(Hyung Joon Ahn); 신평우(Pyung Woo Shin); 박로광(Nho Kwang Park); 김학민(Hak Min Kim) |
| Abstract |
Mechanical properties of multi-step forged Alloy 718 are affected by the processing parameters, such as upset ratio, temperature and holding times for forging, and post heat-treatment. The aim of this study is to find processing conditions to enhance mechanical properties of Alloy 718 pancakes at elavated temperatures up to 700℃. A double step forging process is employed, i.e., firstly at 980℃ or 1025℃, and then at 980℃. Finally, aging treatments are conducted to enhance the mechanical properties through γ´ or γ˝ precipitation. Since the grain size is controlled by the presence of δ phase, the grain size of the pancakes is affected by forging temperature especially near the δ solvus temprature, 980℃. Dynamic recrystallization becomes prominent with increasing temperature for the first step forging, leading to greater grain size and uniform size distribution with increasing temperature. The microstructure after the second step forging at 980℃ and the aging treatment retains the general feature of the microstructure of cat the first step forging, and tensile properties are similar with increasing first step forging temperature. |