Behavior and Mechanism of Void Welding Under Thermal Mechanical Coupling

Abstract

Shrinkage cavity, microporosity, blowhole and the likes are the typical void defects in ingot. Only through reasonable high temperature deformation and heat preservation process can the void defects be closed and welded to ensure the high quality of forgings. However, there are few researches on the welding behavior of voids, and the understanding of the void welding mechanism is still insufficient. In order to further study the welding behavior of void and explore the welding mechanism, the welding process of void and microstructure evolution around void under thermal mechanical coupling were studied by physical simulation. The results show that heating temperature, holding time, plastic deformation play an important role in void welding. The void welding degree increases with the increase of heating temperature, holding time and plastic deformation. Besides, there are three main welding mechanisms for void defects, including the volume of microvoids decreases due to vacancy diffusion, the void welding mechanism caused by the austenite-ferrite transformation at lower temperatures and the void welding mechanism caused by recrystallization and grain growth of austenite grains at higher temperatures.