AFS/FEF Student Technology Contest


Editor’s note: The American Foundry Society and Foundry Education Foundation (FEF) have inaugurated the Student Tech- nology Contest to recognize excellence in metalcasting related research and activities of undergraduate and graduate students in the FEF school network and other schools with metalcasting related programs. FEF scholarships were awarded to the first and second place winning projects, The Development of Ultrahigh Yield Strength Cast Steels with Increased Impact Toughness, submitted by Paul Lynch, Pennsylvania State University, and Grain Refinement of Pure Aluminum Using Ultrasonics by Cory Allen, Purdue University. These two projects, along with an honorable mention project, Microstructure of High-Performance Pure Al/Nano-Si3


N4 by Fei He, Purdue University, have been adapted for publication in the IJMC.


THE DEVELOPMENT OF ULTRAHIGH YIELD STRENGTH CAST STEELS WITH INCREASED IMPACT TOUGHNESS


P. Lynch—PhD. Student Penn State University, University Park, PA, USA Copyright © 2011 American Foundry Society Background


Development work is being carried out by the Penn State Metal Casting Research Group on the next generation of ul- trahigh strength cast steels with improved impact toughness (Figure 1). Until now, the development of UHSLA (ultra- high strength low alloy) steels has mainly been dominated by the development of wrought alloys. Cast alloy develop- ment has lagged behind. A huge potential exists both for defense and commercial applications if affordable UHSLA cast steels can be developed with ultrahigh strength and improved impact toughness. UHSLA cast steels possess lightweight performance as a result of their high strength- to-weight ratio. UHSLA steels are much cheaper to produce than titanium alloys and highly alloyed steels containing large amounts of expensive alloying elements such as nickel and cobalt. UHSLA cast steels can be procured with more ease from a robust network of suppliers. In an attempt to capitalize on these advantages of UHSLA cast steels, there has been renewed interest in the development of ultrahigh strength cast steels with improved impact toughness levels while also possessing ultrahigh strengths. 4340 steel is con- sidered the industry standard for which ultrahigh strength steel comparisons are commonly made. When conventional- ly heat treated (Q&T), UHSLA steel alloys such as 4340 and 8640 typically exhibit acceptable strengths at the expense of acceptable impact toughness and vice versa. When the high


International Journal of Metalcasting/Winter 11


fracture toughness highly alloyed steels (HP-9-4-30 and AF 1410) were developed to exhibit both acceptable strength and impact toughness using standard heat treatment prac- tices, one main problem was the very high cost of the alloys. In addition to the alloying elements contained in the UHSLA steel family, both alloys also contain large amounts of high cost Ni and Co. Initial work has been completed on invest- ment cast 4340+ (silicon modified 4340 steel) steel at Penn State. Austempering, homogenization, and hot isostatic pro- cessing (HIP) studies have been carried out on investment cast 4340+ steel. HIP has significantly improved the impact toughness of the 4340+ alloy while austempering and bainite formation has significantly improved the impact toughness at the expense of strength (Figure 2). Along with HIP quan- tification studies, alloy development work is also being car- ried out on Fe-C-W containing UHSLA cast steels at Penn State. Fe-C-W UHSLA cast steels have the potential to both produce yield strength values above 180ksi at a reduced al- loy cost, while also exhibiting impact toughness values that are far superior to the current generation of UHSLA cast steels (Figure 3).


Acknowledgements


Thank you to Rachel Abrahams and Dr. Voigt for their un- ending support on this project. This project is part of the American Metalcasting Consortium’s Castings for Im-


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