The 1010 steel with 0.2% misch metal addition had a higher yield strength and elongation than the baseline as-cast 1010. The average yield strength for these samples was 195 MPa, and the average percent elongation was 37%. It also had the finest structure of all the 1010 samples examined. The small- er grain size is consistent with the misch metal acting as a grain refiner. An improvement in elongation is consistent with reported findings in aluminum alloys that have been grain refined.14,15
Figures 15-19 are representative micrographs of the 1030 samples without a powder addition. Like the 1010 samples, the 1030 samples with a La2
significantly different enough to warrant inclusion. O3
The 1030 sample with 0.1% RE silicide had a finer structure than the baseline 1030 material. The free fer- rite within the microstructure did not appear to be appre- ciably smaller than the baseline material. However, the distance between the free ferrite is less than the baseline 1030. The pearlite colony size decreased in these sam-
powder addition were not
The structure of the 1030 steel with 0.2% RE silicide was similar to that of the baseline 1030 sample (Figure 17). This is consistent with a grain or pearlite colony size dominant strengthening mechanism since the two materi- als had similar mechanical properties. It should be noted, while this sample had a higher RE content than the 0.1% RE silicide and 0.1% misch metal sample, refinement did not occur.
ples. Other researchers have found a decrease in pearlite colony size can increase strength.16,17
This reduction in
distance between adjoining free ferrite and smaller pearl- ite colony size strengthened the material. It is possible that both are caused by a reduction in the prior austenite grain size through heterogeneous nucleation. However, it is also plausible the rare earth elements affected carbon diffusion during the eutectoid reaction and created the ob- served structure. This had been found with other alloying elements in steel.16
Evidence in the optical microscopy
and tensile testing results is insufficient to develop a de- finitive conclusion.
Figure 14. Micrograph of 1010 with 0.2% MM sample.
Figure 16. Micrograph of 1030 with 0.1% RS sample.
Figure 15. Micrograph of as-cast, baseline 1030 sample. 58
Figure 17. Micrograph of 1030 with 0.2% RS sample. International Journal of Metalcasting/Spring 2012
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