Solidification Sequence of Ferritic and Duplex Stainless Steels Revealed by Liquid-tin Quenching

Weld Crack Susceptibility of Duplex Stainless Steels (Report III)

Abstract

Solidification sequence of ferritic and duplex stainless steels was investigated by freezing the solidification microstructure with liquid-tin quenching during GTA welding. The features of solidification sequence observed are as follows:
(1) A solid bridge formed at very high temperature near the solidification front due to the mutual contact with tips of adjacent secondary dendrite arms.
(2) Residual liquid droplets were confined to the intersectional site of the primary and the secondary dendrite arm boundaries.
(3) In the weld metal which solidified with only ferrite, cellular dendrites were rapidly obscured as temperature decreases even within Solidification Brittleness Temperature Range. Especially, the obsculation of the secondary dendrite arm boundary was much easier than the primary dendrite arm boundary.
These features can not be explained by the application of the unidirectional solidification model.