Single-phase ferritic solidification mode in austenitic-ferritic stainless steel welds

The macro- and microstructures of about 50 different stainless welds of the AISI/AWS 300 series are analyzed. The results indicate that under conditions corresponding to a typical SMA welding, those and only those welds in which the ratio Cr_eq/Ni_eq?1.95, where Ni_eq and Cr_eq are the nickel and chromium equivalents on the Schaeffler diagram, solidify as single-phase ferrite: Austenite subsequently forms from ferrite in the solid state by a Widmanstätten mechanism. The microstructure at room temperature (RT) is characterized by straight phase boundaries and a distinct orientation relationship between the austenite and ferrite. The compositional differences observed at RT are mainly a consequence of the solid state transformation, not of solidification.