Delta Ferrite Segregation
Delta ferrite segregation is a local enrichment of ferrite-stabilizing elements that keeps delta ferrite metastable in the microstructure even at room temperature. This often occurs in high-alloy chromium-nickel steels.
Physical-Chemical Mechanism of Action
Delta ferrite segregation refers to the local enrichment of ferrite-stabilizing elements such as nickel or chromium in the metal. These enrichments prevent delta ferrite from transforming to austenite at room temperature, leaving it metastable.
Metallurgical Relevance & Welding Risks
This metastable phase can lead to increased hardness and reduced ductility. With incorrect welding treatment, such as too rapid cooling or insufficient melt time, delta ferrite can increase and impair mechanical properties.
Workshop Practice & Instructions
To avoid delta ferrite segregation, ensure sufficient melt time (at least 10 seconds per mm thickness) and controlled cooling. For high-alloy chromium-nickel steels, use special welding processes like TIG welding with a protective gas atmosphere.