Representative micrographs of the HK samples are present- ed in Figures 8 and 9. The structure was comprised of aus- tenite and carbides at the dendrite boundaries. More carbides were present than the 304 samples due to the higher carbon and alloy content.
The SDAS was measured using the same procedure as the 304 samples. The ZrO2
the same as the no addition samples. A slightly lower SDAS than the baseline no addition material was noted for the MgO containing samples.
O3
samples. However, results from the MgO samples are incon- sistent with this theory and contradicts the 304 results. It is possible that the significantly higher chromium and nickel content of HK is the reason for this discrepancy. However, there is insufficient evidence in these experiments or the lit- erature to explain this paradox.
The theory proposed about the SDAS being controlled by the cooling rate once solidification starts would explain the average SDAS measurements for the La2
O3 conclusion
This paper examined several possible heterogeneous nuclei using a thermal analysis technique. The undercooling to ini- tiate solidification decreased for the additions of MgO, NbO, NiAl, and TiC in 304. Additions of MgO, La2 in HK also produced undercooling reductions. ZrO2
O3
, and NbO addi-
tions had no effect on the undercooling or secondary den- drite arm spacing of HK. In 304, the secondary dendrite arm spacing was unaffected by the addition of the heterogeneous nuclei. The high cooling rate of the thermal analysis cups likely played a more significant role in determining dendrite arm spacing. Secondary dendrite arm spacing was found to decrease in HK samples with MgO additions.
acknowledgements
The author would like to acknowledge the financial support for this work from the U.S. Navy’s Office of Naval Research under award number N000140811052. The author would also like to thank Lenard Noel and Jeremiah Winkel for their significant contributions in conducting and analyzing these experiments. Lastly, the author thanks Jennie Tuttle for her editorial efforts.
references
1. Beddoes, J., Parr, J. G., Introduction to Stainless Steels, p. 128, ASM International, Materials Park, OH (1999).
2. Kearns, M. A., Cooper, P. S., “Effects of Solutes on Grain Refinement of Selected Wrought Aluminum Alloys,” Materials Science and Technology, vol. 13, no. 8, pp. 650-654 (1997).
International Journal of Metalcasting/Winter 2012 and NbO samples had an average SDAS
slightly larger than the no addition samples which is con- sistent with the lack of undercooling decrease. The average SDAS for the La2
and NbO samples were approximately
3. Lee, Y. C., Dahle, A. K., St. John, D., “The Role of Solute in Grain Refinement of Magnesium,” Metallurgical and Materials Transactions A, vol. 31A, no. 11, pp. 2895-2906 (2000).
4. Gruzleski, J. E., Microstructure Development During Metalcasting, p. 48, American Foundry Society, Schaumburg, IL (2000).
5. Easton, M., St. John, D., “Grain Refinement of Aluminum Alloys: Part II. Confirmation of, and a Mechanism for, the Solute Paradigm,” Metallurgical and Materials Transactions A, vol. 30, pp. 1625-1633 (1999).
6. Bramfitt, B., “The Effect of Carbide and Nitride Additions on the Heterogeneous Nucleation Behavior of Liquid Iron,” Metallurgical Transactions, vol. 1, pp. 1987-1995 (1979).
7. Jackson, W.J., “Control of the Grain Structure in Austenitic Steel Castings,” Iron and Steel, vol. 45, no. 2, pp. 163-172 (1972).
8. Roberts, T.E., Kovarik, D.P., Maier, R.D., “The Solidification and Grain Refinement of Cast Austenitic Stainless Steels,” Transactions of the American Foundrymen’s Society, vol. 87, pp. 279-298 (1979).
9. Van der Eijk, C., and Walmsley, J., “Grain Refinement of Fully Austenitic Stainless Steels Using a Fe-Cr- Si-Ce Master Alloy,” Proceedings of the 59th Furnace Conference, pp. 51-60 (2001).
Electric
10. Ferry, M., Hunter, A., Strezov, L., Mukunthan, K., “Influence of Titanium Inoculation on the As-cast Microstructure of Ferritic Stainless Steel Strip,” Proceedings of Engineering Materials 2001, pp. 33-38 (2001).
11. Ohno, M., Matsuura, K., “Refinement of As-cast Austenite Microstructure in S45C Steel by Titanium Addition,” ISIJ International, vol. 48, no. 10, pp. 1373-1379 (2008).
12. National Institute of Materials Science, “Pauling File: Atomworks,”
http://crystdb.nims.go.jp/index_en.html (28 December 2010).
13. Valdez, M. E., Shibata, H., Cramb, A. W., “Controlled
Undercooling of Liquid Iron in Contact with ZrO2 and MgO Substrates under Varying Oxygen Partial Pressure,” Metallurgical and Materials Transactions B, vol. 37B, pp. 959-965 (2006).
14. Suito, H., Ohta, H., Morioka, S., “Refinement of Solidification Microstructure and Austenite Grain by Fine Inclusion Particles,” ISIJ International, vol. 46, no. 6, pp. 840-846 (2006).
15. Stefanescu, D. M., Science and Engineering of Casting Solidification, p. 131, Springer, New York, NY (2009).
16. Tuttle, R. B., “Grain Refinement in Plain Carbon Steels,” Proceedings of the 114th
Metalcasting Congress, American Foundry Society (2010).
17. Guo, W., Zhang, L., Zhu, M., “Modeling on Dendrite Growth of Medium Carbon Steel during Continuous Casting,” Steel Research International, vol. 81, no. 4, pp. 265-277 (2010).
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