Sulphide and Its Effect on Solidification Cracking in Weld Metal of Steel (Report 1)

Fundamental Investigation on Sulphides in Fe-S Binary Alloy

Abstract

Shape and distribution of sulphides formed in TIG-arc weld metals of Fe-S binary alloys have been investigated. In these alloys the sulphur contents were purposefully much higher than those encountered in commercial steels to make the observation of sulphides easy. Main conclusions obtained are as follows:
1) Two types of iron sulphides, that is, filmlike and globular sulphides are formed in weld metal.
2) Amount of sulphides does not vary from the fusion boundary to the weld center.
3) Filmlike sulphide is generally formed at columnar grain boundary. On the other hand globular sulphide is formed at cell boundary or cellular dendrite boundary.
4) In general sulphides at columnar grain boundary was observed to be more in quantity than at cell boundary or cellular dendrite boundary.
5) Solidification crack occurs along the filmlike sulphide at columnar grain boundary. No crack is observed along the globular sulphide.
6) It was considered to be due to the difference between the grain boundary energies that the shape of sulphide at columnar grain boundary was different from that at cell boundary or cellular dendrite boundary.