Use of a mechanical properties microprobe in the study of weld transformations
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Specimen Diameter, or Thickness, to Grain Size Ratios for Large Grain-Size Ni3A! Alloys Compression Specimen Diameter, or Thickness, mm 12.7 ? 6.35 6.35** 6.35 2.0 6.35 3.0 3.0
Reference Schulson, Weihs, Viens, and Baker4 Flinn lo 9 Davies and Stoloff" * Grala ~29 Thornton, Davies, and Johnston 13* Lopez and Hancock ~4. Marcinkowski and CampbeW5. Aoki and [ z u m i 16 * Noguchi, Oya, and S u z u k i 17 *
Grain Size mm 0.9 to 1.1 1.0 0.5 1.0 0.8 1.0 0.6 0.8 0.8
Specimen Diameter or Thickness Grain Size 11.5 to 14.1 -12.7 6.3 7.9 2.0 10.6 3.7 3.7
? Not given in the reference. * Reference numbers as given in Reference 4. ** Tensile specimen.
veloped by Thompson et al. s At very large grain sizes, 'statistically stored dislocations' dominate the behavior, as opposed to 'geometrically necessary grain boundary dislocations' because of a relatively small size of grain 'skin' in large-grained materials. 8 In fact, the yield strength (0.2 pct) vs (grain size) -v2 curve computed according to this model for aluminum extrapolates to a negative intercept on the ordinate.
REFERENCES 1. W.M. Baldwin: Acta Metall.. 1958, vol. 6, pp. 139-41 2. J_ P. H~rth: Metall. Trans.. 1972, vol. 3, pp. 304%67. 3. A R. Marder and B.L. Bramfin: Metall. Trans. A, 1976, vol. 7A, pp. 365-72. 4 E.M. Schulson, T. P Weihs. D. V. Viens, and I. Baker: Acta Metall., 1985, vol. 33, pp 1587-91. 5. J.M. Hyzak and I.M. Bemstein: Metall. Trans. A, 1976, vol. 7A, pp. 1217-24. 6. A. W. Thompson: Scripta Metall., 1974, vol. 8, pp. 145-48. 7. M . A . Meyers and K . K . Chawla: Mechanical Metallurgy, Principles and Applications, Prentice-Hall, Inc , Engelwood Cliffs, NJ 07632. 1984, p. 494. 8. A.W. Thompson, M.I. Baskes, and W. E Flanagan: Acta Metall, 1973. vol. 21, pp. 1017-28.
Use of a Mechanical Properties Microprobe in the Study of Weld Transformations S. A. DAVID, I. M. VITEK, J. R. KEISER, and W. C. OLIVER Specifications for austenitic stainless steel weld metal call for varying amounts of ferrite to be present in the microstructure of the room-temperature weld metal. When present, ferrite has been found to effectively prevent hot cracking in the weld metal.l"2'3 Therefore, most austenitic stainless steel weld metal contains a duplex austenite plus ferrite (3/ + 6) microstructure with the ferrite content varyS.A. DAVID, Group Leader, and J.M. VITEK, J R, KEISER, and W.C. OLIVER, Members, Research Staff, are with Oak Ridge National Laboratory, P.O. Box X, Oak Ridge. TN 37831-6156. Manuscript submitted December 16, 1986. 1996--VOLUME 18A, NOVEMBER 1987
ing from 5 to 40 pct in volume, depending on the composition. When welds containing this duplex structure are exposed to elevated temperatures (550 to 850 ~ a variety of transformations have been found to occur. 4'5 The first transformation observed upon aging type 308 stainless steel welds at temperatures in excess of 550 ~ is the formation of M23C6 carbide at the ferrite-austenite interface. 4 With further aging, ferrite consolidation occurs. Extensive solute redistribution resulting in the enrichment
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