The observation and identification of the oxide film on the creep cavity wall of type 316L stainless steel
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Creep cavities in type 316L stainless steel are usually found in the grain boundaries or triple junctions. The nucleation and growth rate of such creep cavities are known to depend on the surface energy.[1,2,3] The critical radius, rC, from which the embryo cavity could grow as a stable creep cavity is as follows:[4] rC
Fig. 4—Fracture surface of a failed Cr-2Ag specimen.
titial impurities, such as nitrogen, during the melting processing. Adding Ag may also decrease the DBTT of Cr low enough to exhibit ductility at room temperature, because Ag meets the selection condition of the solute atoms by adding to the decrease of DBTT.[11] Future work should be done to clarify the role of Ag in the ductile Cr-Ag alloys.
The authors thank S Nishi and T. Kusamichi, Kobel Steel, and T. Kobayashi, NIMS, for their help in chemical analysis. REFERENCES 1. A.H. Sully: Metallurgy of the Rarer Metals—1. Chromium, 1st ed., Butterworths Scientific Publications, London, 1954, pp. 254-268. 2. W.D. Klopp: J. Met., 1969, vol. 21, pp. 23-32. 3. E.S. Greiner: Trans. AIME, 1950, vol. 188, pp. 891-892. 4. N.I. Medvedeva, Y.N. Gornostyrev, and A.J. Freeman: Acta Mater., 2002, vol. 50, pp. 2471-2476. 5. A.H. Sully and E.A. Brandes: J. Inst. Met., 1952-53, vol. 81, pp. 573-577. 6. A.H. Sully, E.A. Brandes, and K.W. Mitchell: J. Inst. Met., 1952-53, vol. 81, pp. 585-598. 7. F. Henderson, S.T. Quaass, and H.L. Wain: J. Inst. Met., 1954-55, vol. 83, pp. 126-132. 8. G.R. Wilms and T.W. Rea: J. Less-Common Met., 1959, vol. 1, pp. 152-156. 9. W.P. Rees, B.E. Hopkins, and H.R. Tipler: J. Iron Steel Inst., 1951, vol. 169, pp. 157-163. 10. W.H. Smith and A.U. Seybolt: Ductile Chromium and Its Alloys, 1st ed., AMS, Cleveland, OH, 1957, pp. 169-179. 11. O.N. Carlson, L.L. Sherwood, and F.A. Schmidt: J. Less-Common Met., 1964, vol. 6, pp. 439-450.
The Observation and Identification of the Oxide Film on the Creep Cavity Wall of Type 316L Stainless Steel YONGBOK LEE, DOKYOL LEE, JINSUNG JANG, and WOO-SEOG RYU Type 316 L stainless steel specimens were creep rupture tested at 620 °C in a vacuum. The FeO type wüstite phase with the lattice parameter of about 4.056 Å was identified on the creep cavity wall. The {200} planes of the oxide phase have shown the epitaxial growth on the {111} planes of the matrix phase. As the oxide film forms on the creep cavity wall, the surface energy term of the cavitation could METALLURGICAL AND MATERIALS TRANSACTIONS A
2g 2ds s 3E
where is the applied stress, the specific surface energy, d the average grain diameter, and E the Young’s modulus. The cavity growth rate by diffusion also has been derived as[5] 2pdDgb[s (2g/r)] dV
a dt kT where is a cavity size-spacing term, the atomic volume, the grain boundary width, Dgb the gain boundary diffusion coefficient, and kT the thermal energy. As the surface energy decreases, the critical radius of cavity decreases and the cavity growth rate increases. Although the significance of the surface energy for the cavity nucleation rate of pure metal, or the important role o
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