Effect of yttrium treatment on alumina inclusions in high carbon steel

Aluminum oxide inclusions in SWRS82B steel seriously affect the drawing performance of steel strands. The effects of different addition amounts of yttrium (within the range of 0%–0.026%) on the composition, morphology, size and spacing of aluminum oxide inclusions were studied by scanning electron microscopy and energy spectrum analysis. Based on classical thermodynamics and FactSage software, the predominance diagram of inclusions in Fe–O–S–Y system and the effect of the addition of rare earth yttrium on the stability of alumina inclusions were calculated. The results showed that molten steel was modified by adding the rare earth element yttrium. It can be inferred that the approximate route of target inclusion modification was: Al2O3 → Y2S3 + YAlO3 + Al2O3 → Y2S3 + YAlO3 + Y2O2S + YAlO3 + Al2O3 → Y2S3 + Y2O2S. The experimental samples with 0.026% added yttrium had the best inclusion characteristics, in which the inclusion surface density distribution was uniform, and the interfacial distance between inclusions was mainly in the range of 100–500 μm. After modification, the average inclusion size in molten steel was reduced by 6.9–8.6 μm. The mechanism of yttrium modification was discussed based on actual calculation results and experimental results.