Studies of the orientations of fracture surfaces produced in austenitic stainless steels by stress-corrosion cracking an
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1. I N T R O D U C T I O N
THE orientation studies described in this paper are part of a broad study of the mechanisms of hydrogen embrittlement (HE) and stress-corrosion cracking (SCC) in austenitic stainless steels. 'l'he thrust of this program concerns the role of austenite transformation to a' and c martensites in both phenomena, and the controversial question of whether hydrogen plays a central role in SCC. Both H E and SCC produce transgranular fractures which are crystallographic and cleavage-like in appearance, but it is not known whether the fracture surfaces have a c o m m o n orientation. Previous orientation studies have been confined to SCC. Reed and Paxton ~used two-surface trace analysis to study the orientations of cracks produced in monocrystals of Fe-20Cr-20Ni, Fe-20Cr-12Ni and a commercial type 304 steel (18.4Cr-9.5Ni-0.04C), tested in a boiling aqueous MgC12 solution (154 ~ For Fe20Cr-20Ni, the poles of the stress-corrosion fracture surfaces were found to be clustered around the { 100} pole which was closest to the tensile axis, Fig. 1. The behavior was reported to be quite different for Fe20Cr-12Ni and the type 304 steel. In these cases, the R. LIU, formerly with the Department of Metallurgy, University of Illinois at Urbana-Champaign, is now with the Bell Telephone Company, Murray Hill, NJ. N. NARITA, formerly with the Department of Metallurgy, University of Illinois at Urbana-Champaign, is now with the Department of Metal Science and Technology, Kyoto University. C. ALTSTETTER is Professor of Physical Metallurgy, Department of Metallurgy and the Materials Research Laboratory, University of Illinois at Urbana-Champaign. H. BIRNBAUM is Professor of Metallurgical Engineering, Department of Metallurgy and the Materials Research Laboratory, University of Illinois at Urbana-Champaign. E. N. PUGH, formerly Professor of Metallurgy, University of Illinois, is now with the National Bureau of Standards, Washington, D.C. Manuscript submitted November 26, 1979.
fracture plane was again approximately normal to the tensile axis but was reported as "not obviously associated with a crystallographic plane"; the data for these specimens are also shown in Fig. 1. Examination of the fracture surfaces with the TEM, using an oxide replica technique, indicated that they were relatively flat for Fe-20Cr-20Ni, but those for Fe-20Cr-12Ni and type 304 were described as being "made up of small facets, possibly crystallographic, which are less than 1/~m in size." Marek and H o c h m a n 2 also used two-surface trace analysis to determine the fracture plane for monocrystal specimens of type 316 steel (16.2 Cr, 13.7 Ni, 2.86 M o and 0.02 C), tested in boiling aqueous MgC1 z 0 5 5 ~ The results, Fig. 1, indicated that the orientation of the fracture plane was at or very close to {210}. SEM examination of the fracture faces indicated that they possessed the characteristic cleavage-like appearance, now observed by numerous workers, see Fig. 2. Despite the faceted nature of the surfaces, the authors considered that "it is har
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