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Figure 18 presents the microstructure of the 1030 sample with 0.1% misch metal. The free ferrite grain size is significantly smaller than the baseline 1030 material. The free ferrite also was more rounded. The reduction in grain size is consistent with a grain size reduction strengthening mechanism for this al- loy. For the 1030 0.1% MM sample, the average yield strength was 296 MPa compared to 262 MPa for the baseline material.


Samples of the 1030 0.2% misch metal addition exhibited a fine grain structure and the highest strength (See Figure 9). The free ferrite had a significantly smaller grain size than the baseline material.


Electron Microscopy


An SEM with EDS was used to investigate the inclusions found in the rare earth-containing steels. Figure 20 depicts a typical oxide inclusion in the 1010 0.1% RE silicide sample. The gray region had a high RE content with about 11% alu- minum. EDS analysis of the dark region indicated an alumi- num-iron oxide with a small amount of cerium.


The inclusion depicted in Figure 21 from the 1010 0.2 % RE silicide sample contained an inner gray region with a combination of a high RE content and around 2% alu- minum. This region also contained 8% sulfur. The dark region surrounding most of the inner gray region is an aluminum-iron oxide.


Figure 22 presents an inclusion in the 1010 0.1% misch met- al sample. Many of the RE inclusions were rounded. The inclusion at the lower left has an inner light gray area sur- rounded by a darker gray. The light gray area consisted of a RE oxide with approximately 13% aluminum, while the darker gray area had a lower RE content and an aluminum level of 30%.


A common oxide inclusion for the 1010 0.2% misch metal sample is illustrated in Figure 23. The gray region has a high RE content with 11% aluminum. The dark region sur- rounding half of the inclusion consisted of an iron-alumi- num oxide.


Figure 18. Micrograph of 1030 with 0.1% MM sample.


Figure 20. Image of a typical inclusion from the 1010 0.1% RS sample.


Figure 19. Micrograph of 1030 with 0.2% MM sample. International Journal of Metalcasting/Spring 2012


Figure 21 SEM image of oxides from the 1010 0.2% RS sample.


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