Effect of Mg-Bearing Oxide( plus TiN) Inclusion on Microstructure of Fe-16 Mass Pct Cr Ferritic Alloy and Its Evolution During Heating at 1573K (1300°C)

Both the effects of Mg-bearing oxide and Mg-bearing oxide+TiN inclusions on the microstructures of Fe-16 mass pct Cr alloy should be clarified. In this paper, the effects of Mg-bearing oxide(+TiN) inclusions on the microstructures of Fe-16 mass pct Cr ferritic alloy and changes due to the inclusions during heating at 1573K (1300 degrees C) were studied by manual and automatic SEM-EDS analyses. Three alloys were used as specimens. The inclusions were Al2TiO4+TiN with a small amount of TiN in alloy #1, Al-2(Mg, Ti)O-4 in alloy #2 and Al-2(Mg, Ti)O-4+TiN in alloy #3. The average grain size was smaller, and the ratio of columnar grains was lower in the as-cast alloy #2 and as-cast alloy #3 than that in the as-cast alloy #1. This is attributed to the heterogeneous nucleation of delta ferrite on Al-2(Mg, Ti)O-4 during solidification. Refinement of the microstructures of ferritic steel by Mg-bearing oxide+multi-TiN inclusions is proposed. Changes in composition, aspect ratio, and size distribution of inclusions in each alloy during heating were investigated systematically. Mg-bearing oxide(+TiN) was dispersed in both the as-cast alloys and heated alloys, which contributed to microstructural refinement of the heated alloys through the pinning effect.