Analytical scanning transmission electron microscopic study on metastable modulated structure in a rapidly quenched Fe-2
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Mechanical Properties of Alloy Modifications
Alloy
Stress Rupture Life (Hours)* (655 MPa/732 ~
YS (MPa)
A-1 A-2 A-3 A-4
58 47 31 55
1080 1076 1083 1070
B-I B-2 B-3 B-4
22 16 43 53
1103 1117 1089 1110
Tensile Results UTS (MPa) EL (Pct) 704 ~ 1283 17.0 1282 20.0 1298 20.0 1274 18.0 538 ~ 1517 23.5 1530 23.3 1482 28.0 1509 26
RA (Pct) 18.3 21.1 19.7 20.4 19.8 21.6 24 25
*Average of three tests
It is important to note that the chromium level of the matrix depends not only on the alloys' bulk chromium level, but also upon all other alloying elements. For example, the 7'-forming elements (A1 + Ti) will increase the matrix's chromium level by removing nickel from the matrix to form Ni3(A1, Ti). There are undoubtedly more complex interactions that affect the matrix's chromium level such as the effect of cobalt on the volume fraction of 3". As the volume fraction of 3" changes with the cobalt level, so does the amount of nickel removed from the matrix to form Ni3(A1, Ti). 5 This results in a change in the matrix's chromium saturation. Although these secondary chemistry considerations are difficult to document, they are expected to affect the formation of the carbide phase. In summary, we have observed that subtle changes in the alloys' matrix chemistry result in a significant effect on the precipitation of a continuous M23C6 carbide phase during the 760 ~ segment of the heat treatment. In addition, the carbon content of the alloy was observed to have relatively little influence on the formation of the continuous carbide for concentrations of 0.03 to 0.09 wt pct. The explanation of these effects of alloy chemistry on the formation of the continuous carbide is believed to involve the degree of saturation of chromium in the matrix. At higher matrix chromium levels there is a stronger driving force for the formation of the M23C6 phase, and the partitioning of carbon shifts from the MC carbide to the M23C6 carbide. The appearance of the continuous M23C6 carbide can therefore be controlled by maintaining a lower saturation of the matrix with respect to chromium.
Appreciation is extended to B. Quimby of Homogeneous Metals Inc. for the atomization of the alloy powders, and to S.G. Berkley for helpful discussions on the role of alloy chemistry.
4. L.A. Jackman, H.B. Canada, and E E. Sczerzenie: in Superalloys 1980, Proceedings of the Fourth International Symposium on Superalloys, ASM Publications, Metals Park, OH, 1980, pp. 365-74. 5. C. P. Sullivan and M. J. Donachie, Jr.: in Source Book on Materials for Elevated Temperature Applications, ASM Publications, Metals Park, OH, 1979, pp. 250-59.
Analytical Scanning Transmission Electron Microscopic Study on Metastable Modulated Structure in a Rapidly Quenched Fe-22Ni-8AI-2.4C Alloy A. INOUE, L. ARNBERG, B. LEHTINEN, and T. MASUMOTO Inoue et al. ~.2 have found in 1979 that Fe-Ni-AI-C and Fe-Mn-A1-C alloys prepared by melt spinning exhibit a high tensile fracture strength (o-I) reaching about 1700 MPa combined with an elongation (%) of about 5 pct, even in a ribbon with a
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