Phase Relations in Ce-AI-Fe-S Based Grain Refiners for Steels

摘要

In the present investigation the phase relations within the Ce-Al-Fe-S system have been clarified, using a combination of optical microscopy and WDS microprobe analyses. As a starting point high-purity charge materials of cerium, aluminium and FeS_2 are melted and superheated to about 2 000℃ within small tantalum crucibles inside a dedicated laboratory furnace filled with cleaned argon. The phases detected in the as-solidified samples were CeS, Ce_3Al, Fe_2Ce and γ-Ce, along with Ce_2O_2S, which is an undesirable microcon-stituent in CeS-based grain refiners. It is concluded that FeS_2 can be used as a sulphur source for addition up to about 4 wt% sulphur. At higher levels the Fe-Ta interaction becomes so vigorous that tantalum no longer acts as an inert refractory metal and wetting becomes a major problem. In contrast, aluminium is an essential alloying element in the sense that it prevents the grain refiners from disintegrating in contact with air due to internal oxidation of free cerium by promoting the formation of Ce_3Al.