Residual Delta Ferrite
Residual delta ferrite is a high-temperature ferrite that remains metastable due to rapid cooling or strong alloying influences and is retained in the microstructure down to room temperature.
Physical-Chemical Mechanism of Action
Residual delta ferrite forms upon rapid cooling of high-temperature ferrites or due to strong alloying influences. It is metastable and retains its structure down to room temperature.
Metallurgical Relevance & Risks in Welding
Residual delta ferrite can lead to increased hardness and reduced toughness, impairing the mechanical properties of the steel. It can also lead to cracks and hot cracks, especially in heavily loaded components.
Workshop Practice & Action Instructions
To minimize residual delta ferrite, controlled cooling is required. Use a long cooling path or add stabilizing elements like silicon. Pay attention to correct alloying and the right welding process.