13. Suito H., Ohta H., and Morioka S., “Refinement of So- lidification Microstructure and Austenite Grain by Fine Inclusion Particles,” ISIJ International, vol. 46, no. 6, pp. 840-846 (2006).
14. Krauss G., Steels: Processing, Structure, and Perfor- mance, p.121, ASM International, Materials Park, OH (2005).
15. Vander Voort G. F., Metallography: Principles and Practice, p. 218, McGraw-Hill, New York (1984).
16. Goldstein J., Scanning Electron Microscopy and X-ray Analysis: A Text for Biologists, Materials Scientists, and Geologists, 2nd (1992).
17. Villars P., Pauling File, 1995,
http://crystdb.nims.
go.jp/, (2 March, 2009).
18. Introduction to Gray Cast Iron Processing, p. 33, American Foundry Society, Des Plaines, IL (2000).
ed., p. 88, Plenum Press, New York
Technical Review and Discussion
Examination of Steel Castings for Potential Nucleation Phases Robert Tuttle, Saginaw Valley State University, University Center, MI, USA
Reviewer: Many steel foundries use Ti to deoxidize. How- ever, castable 8620 (0.7-1.0% Si) is easily impacted when Ti is >0.010%, which would be seen in reduced fatigue strength. Thin section thickness castings are the future of steel castings and so the steel casting industry must approach with good confidence that processes and procedures are very sound. This is most important in batch induction melting where re-melt and sprues are used as charge materials. Ni- trogen pick-up needs to be controlled as well as oxygen. Ni- trogen analysis can be made but the foundry must use charge material that has known trap elements and controlled chem- istry. Bubbling argon in the furnace or cover gases can also work but it is hard to maintain. The author does not mention these other issues and techniques.
Author: The issues with excessive nitrogen pickup through using high levels of in-plant scrap are certainly
true. In fact, that is the main reason this foundry uses titanium for deoxidation instead of aluminum. Titanium deoxidation allows them to avoid issues with rock candy fracture due to aluminum nitride formation. It would be better to create an induction melting process that utilizes inert gas injection to remove nitrogen. There has been some success in England with using porous plugs in the bottom of induction furnaces. These are the same porous plugs used for argon stirring in steel mill ladles. The author is not aware of anyone in the U.S. using this tech- nique, though. A combination of this technique and using real time nitrogen analysis may lead to a breakthrough in this regard. However, this is not the subject of the cur- rent article or research project.
In terms of forming TiN particles by controlling the titanium and nitrogen content of the heat, the author has not entirely thought through the process necessary to do this. His cur- rent work focuses on determining how to grain refine steels. Using TiN as the nucleating material may simply require purchasing a fine titanium nitride powder. There are also other materials that can act as effective nuclei which would be easier to form in liquid steel. Results from work with these materials will be published at a later time.
International Journal of Metalcasting/Summer 10
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