Secondary Recrystallization of Weld Seam Metal
Welding is widely used in many aspects of industry, and the weld seam metal has a direct relationship with the quality of welding process and the performance of welding materials. The welding process changes the microstructure of the welded metal, resulting in low strength and poor plasticity. The secondary recrystallization of weld seam metal is an important method to improve the mechanical properties.
The secondary recrystallization of weld seam metal is the process of formation of new grain structures and grain boundaries during welding process. In this process, during welding, the high temperature caused by the welding arc and the plastic deformation of the weldment will lead to the recrystallization of the grain in the weldment and the formation of a new grain structure. This process can effectively eliminate the defects caused by coarse grain boundaries in the weldment, improve the mechanical properties of the weldment, reduce the stress concentration and gradually saturate the austenite in the weldment, so as to obtain dense microstructure and good properties.
The performance and microstructure of the welded metal can be controlled by controlling the heat input during welding process. The size of the cooling rate and the size of the thermo-mechanical cycle have a great influence on the recrystallization rate and the microstructure in the weldment. And, at the same time, the materials used have an influence on the second recrystallization of weld seam metal. The welding process should be matched reasonably according to the properties of the materials used, the welding thermal cycle and recrystallization tendency. When the welding current is constant, the width of the welding heat affected zone (HAZ) is related to the welding speed, and the recrystallization rate of weldment is related to the HAZ width and the microstructure at high temperature.
In addition, the surface layer of the weldment has a great influence on the secondary recrystallization of the weldment. The characteristics of surface melt droplets further affect the recrystallization rate and grain size of the weldment near the surface layer. In order to reduce the grain size of the weldment, the non-metallic particles or reinforcement materials can be added to the surface layer before welding to affect the surface melt droplets and influence the secondary recrystallization of weldment.
The secondary recrystallization of weld seam metal is an important process to improve the mechanical properties of weldment. The rate and microstructure of the recrystallized metal can be changed through controlling the heat input during welding process and the materials used, and the weldments can be prevented from decarburization by properly controlling the characteristics of surface melt droplets.
