1997 Volume 15 Issue 2 Pages 281-291
Solidification behaviors of austenitic stainless steel weld metals near fusion boundaries were studied, in which the epitaxial growth and the selection of primary phase were of main interest. In the AF solidification mode, planar austenite grows epitaxially from austenite grains in the base metal. Subsequently ferrite forms at dendrite boundaries of the primary austenite after the austenite changes from planar to dendritic. In the FA solidification mode, planar austenite grows epitaxially from austenite grains in the base metal as a result of competition between ferrite nucleation and austenite growth. Then ferrite nucleation is followed because of the enrichment of Cr in the liquid, and continues to grow eventually as the primary phase. The ferrite has the K-S relationship with the planar austenite. In the stage of primary ferrite solidification, austenite sodilifies as the second phase at dendrite boundaries, and has the same crystallographic orientation as the original planar austenite. In the sample which solidifies as FA mode with the lowest Cr/Ni ratio, it is possible for austenite to solidify even as the primary phase because of the fluctuations of solutes in the liquid and the change of undercooling due to local change in temperature gradient in the liquid.
