different with the grain structure in the hourglass shaped bars being finer than the carrot shaped bars. The mechanical testing results from the two types of bars were also different, with the hourglass shaped bars passing all stress rupture requirements and the carrot shaped bars failing either the rupture life or elongation requirement. The most likely cause for the differences between the test bar types was the difference in the grain structures. While this paper is not meant to give
an exhaustive list of casting conditions and how they impact mechanical test results, the results that were discussed illustrate Cannon-Muskegon’s belief that a fine, equiaxed grain structure will give the most consistent mechanical results that will be representative of the alloys capabilities.
Recomendations It is recommended that casting facilities perform a grain structure characterization on their mechanical test bars as this will help with understanding mechanical test results. This is important even for facilities that are able to consistently pass mechanical test requirements. Having an understanding of the grain structure will be useful in diagnosing problems if unexpected failures begin to occur. In addition, facilities that have variable mechanical results would also benefit from understanding the grain structure of their tensile bars. If the test bars show porosity or coarse grains in the gage section, the variability of the test results may be due to the grain structure.
References Dieter, George JR. Mechanical
Metallurgy, 1961. Campbell, John. Castings, 1991.
Acknowledgements The author would like to gratefully ac- knowledge the help and support he received from Jacqui Wahl and Tony Huiber, both from Cannon-Muskegon Corporation.
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Test Conditions 980ºC/150 MPa
Test Bar Shape Carrot Carrot Carrot Carrot Carrot
Hourglass Hourglass
AMS 5377 Requirements
Rupture Life (h) 22.3 23.8 28.3 26.6 28.4
53.1 58.4
30 h min.
5D Elongation (%) 2.5 3 5 5
2.5 8.5 9.2
4% min.
Table 3: Stress rupture results for Carrot and Hourglass shaped test bars. Failing results are in red.
V ACUUM ALL O Y S / AIRMELT ALL O Y S / ALL OY DEVELO PMEN T / L AB SERVI CES
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