Population Size Distribution of Rare Earth and Non-metallic Inclusions in 4130 and 8630 Steels

Abstract

The purpose of this work was to find the population size distribution of rare earth and non-metallic inclusions in polished samples and filter paper samples of 4130 and 8630 steels. The steels had additions of either rare earth silicide or EGR grain refiner. Interest in rare earth-containing inclusions has increased due to their ability to refine the solidification structure of steel. However, the exact mechanism is not fully understood. To accurately determine size and composition, electrolytic dissolution with 2% TEA was employed to dissolve the steel matrix away. A scanning electron microscope examined the isolated inclusions on filter paper specimens. For comparison, other samples were analyzed in a more typical polished metallographic specimen. All heats had very similar inclusion sizes. Most inclusions were between 5 and 9 μm. There was a variation in inclusion composition between the 4130 and 8630 heats. The cause of this variability appeared to be due to random changes in the amount of reoxidation that occurred during tapping.