Secondary Segregation
Secondary segregation is the local enrichment of alloying elements at grain boundaries or phase boundaries during or after solidification. This can lead to undesirable brittle fracture or localized corrosion susceptibility.
Physico-Chemical Mechanism of Action
Secondary segregation occurs when certain elements concentrate at specific boundaries during cooling or after the solidification process. This can be caused by diffusion phenomena and thermodynamic stresses.
Metallurgical Relevance & Welding Risks
Secondary segregation can lead to unwanted brittle fractures, because the concentrated elements change the structure and make it more prone to cracking. It also increases local corrosion susceptibility, since certain additions promote accelerated oxidation.
Shop Practice & Action Guidelines
To avoid secondary segregation, it's important to carefully control welding parameters like temperature and time. Use proper shielding and keep the weld pool clean. For special steels or alloys, a prior heat treatment (tempered heat treatment) can help regulate diffusion processes.