Duplex Ferrite Phase Volume Fraction
The quantitative ratio between ferritic and austenitic microstructural constituents in duplex steels to ensure optimal mechanical and corrosion-chemical properties. Determination is typically performed metallographically or magnetically.
Duplex steels have a mixed structure of ferrite and austenite. That gives them high strength and good corrosion resistance. When welding, you have to watch that the ratio of the two structure components in the weld and heat-affected zone doesn't tip too much. If you put in too much heat or cool too slowly, too much austenite can form, making things tough and corrosion-prone. If cooling is too fast, you get too much ferrite, which becomes hard and crack-prone. So you have to keep an eye on the interpass temperature and control the heat input cleanly, then the structure will be right.