Microstructure selection of Fe–Cr–Ni alloy during directional solidification.

Phase and microstructure selection in directionally solidified AISI 304 stainless steel has been theoretically studied using the highest interface temperature criterion to explore primary phase prediction during rapid directional solidification. It is found that competitive growth exists between the stable phase (δ) and the metastable phase (γ) because of different solidification conditions. For the alloy calculated, metastable phase (γ) dendrites begin to precipitate as the primary phase when the growth rate is higher than 4·2 cm s–1 at the given temperature gradient of 300 K mm–1. Strip casting experiments on 304 using a symmetrical water cooled copper mould confirmed the theoretical prediction. The influence of temperature gradient on the velocity scope and the interface temperatures of planar growth and dendrite/cellar growth in directionally solidified stainless steel are also discussed. [ABSTRACT FROM AUTHOR]