Grain boundary migration
The movement of crystal boundaries in a thermal field to reduce total energy, which controls grain growth during annealing.
Physicochemical Mechanism of Action
Crystals in metals grow and enlarge by the diffusion of atoms to their grain boundaries. In a thermal field (annealing condition), these boundaries shift to achieve a minimization of total energy.
Metallurgical Relevance & Risks in Welding
Grain boundary migration affects the microstructure and mechanical properties of the material. Too rapid growth can lead to fine grains, which increases toughness, but also increases the risk of cracks. Too slow growth can lead to coarse grains, which reduces formability and hardness.
Workshop Practice & Action Instructions
To ensure optimal grain boundary migration during welding, pay attention to the following:
• Keep the temperature in the annealing state constant and avoid rapid temperature changes.
• Use suitable shielding gas mixtures to create a homogeneous environment.
• Monitor the cooling duration carefully: cooling too quickly can lead to glass-hard martensite, too slowly to coarse grains.