Effect of Nitrogen on the Formation and Evolution of Non-Metallic Inclusions in Fe–Al–Ti–N Alloy

The effects of nitrogen content on the formation and changing behaviors of non-metallic inclusions in the four kinds of Fe–Al–Ti–N alloys during heating at 1473 K were studied by observation and analysis of inclusions by FE-SEM and EDS. At the inner part of the specimens, TiN-based inclusions were mainly observed. The size of TiN single phase particles observed in as-cast specimens was much larger in the specimens with larger nitrogen content. The fraction of the number of TiN-based inclusions increased by heating in the specimens with larger nitrogen content, while it decreased in the case of smaller nitrogen content due to the formation of TiS inclusions during heating. The growth of TiN single phase particles in larger nitrogen content specimens was more significant than those in smaller nitrogen content specimens. At the outer part of the specimens, TiN formed after heating on the already existing oxide inclusions. In addition, the size of TiN on the oxide surface formed during quenching also increased by heating. The fraction of the number of oxide inclusions with TiN increased in all specimens by heating. TiN phase on the oxide surface in as-cast specimens was bigger in the case of larger nitrogen contents. TiN growth during heating was also enhanced in larger nitrogen content specimens.