Solidification Sequence of Austenitic Stainless Steels Revealed by Liquid-tin Quenching

Weld Crack Susceptibility of Duplex Stainless Steels (Report II)

Abstract

Solidification sequence of austenitic stainless steels, SUS31OS, SUS316L and SUS304L, was investigated by freezing the solidification microstructure with liquid-tin quenching during GTA welding. The results are as follows:
(1) Liquid-tin quenching method had sufficient cooling rate to reveal the solidification sequence, even though the weld metal solidified with the primary ferrite and the subsequent austenite.
(2) The solidification microstructure of SUS310S, which solidified with only austenite, can be evidently observed within Solidification Brittleness Temperature Range. Liquid droplets were confined to the intersectional site of the primary and the secondary dendrite arm boundaries due to formation of a solid bridge near the solidification front.
(3) In SUS316L which solidified with the primary austenite, the subsequent ferrite formed from the same confined liquid during solidification as mentioned in (2). In the case of SUS316L which solidified with the primary ferrite, on the contrary, the subsequent austenite formed from the liquid remaining between primary ferrites. Residual liquid was found at the austenite/ferrite interphases.
(4) SUS304L solidified with the primary ferrite and the subsequent austenite formed at. cellular dendritic boundaries. Residual liquid was found at the center of the austenite.
With the obtained results, solidification sequence of each austenitic stainless steel during solidification could be illustrated in a more detailed fashion.