Crystalline nucleation process
Crystal nucleation is the first step in phase formation where stable submicroscopic units (nuclei) of a new phase form. Overcoming a critical nucleus size is essential.
Physicochemical Mechanism of Action
The crystalline nucleation process begins with nucleation, where submicroscopic nuclei form from a supersaturated state. These nuclei then grow through the diffusion of atoms or ions from the surrounding environment. The process is thermodynamically unfavorable and requires an energy saving.
Metallurgical Relevance & Welding Risks
Insufficient cooling can prevent the crystalline nucleation process from completing fully, leading to fine grains and increased hardness of the structure. This can impair the toughness of the steel and cause cracking. Too fast a cooling process prevents enough nuclei from forming, which can lead to a failed welding operation.
Workshop Practice & Instructions
To complete the crystalline nucleation process successfully, controlled cooling is required. The cooling steps should be designed to overcome the critical nucleus size and provide sufficient time for nucleation and growth of the nuclei. This can be achieved by choosing the appropriate welding process (e.g., TIG welding) and controlling the cooling signals.