Stacking fault energies of seven commercial austenitic stainless steels
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AND
R. P. REED
The stacking fault energies of seven c o m m e r c i a l austenitic F e - C r - N i , F e - C r - N i - M n and Fe-Mn-Ni alloys have been determined by X - r a y diffraction line profile analysis. From comparison with existing data on laboratory alloys with similar compositions, it is coneluded that both Ni and C increase 7 while Cr, Si, Mn, and N d e c r e a s e ~. Regression analysis of data produced in this study provides an expression relating ~ to c o m m e r c i a l alloy composition in terms of Ni, Cr, Mn, and Mo alloy concentrations. T H E stacking fault energy (~) is of both practical and theoretical interest and is reported here for a s e r i e s of commercial austenitic steels. The defect properties of alloys are known to affect mechanical behavior and the stacking fault energy is essential to any fundamental understanding of the defect structure. Stacking fault energy influences dislocation c r o s s slip and climb, which are dominant factors in metal work hardening and creep behavior. The stacking fault energy also affects susceptibility to s t r e s s c o r r o s i o n cracking. 1 In austenitic steels the influence of the stacking fault energy on hydrogen embrittlement must be considered, since Fe-18 Cr-8 Ni (AISI 304) alloys are known to be m o r e susceptible to embrittlement than the m o r e stable Fe-25 Cr-19 Ni (AISI 310) grades, z'3 The stacking fault energy has been previously d e t e r mined for several Ni-base and some Fe-base alloys, mostly binary systems. 4'S The t e r n a r y system F e - C r Ni is important because it is the basis for austenitic stainless steels. Most of the measurements that have been made 6-2~ (Fig. 1) for F e - C r - N i alloys have been on high-purity laboratory melts with carefully controlled compositions. Nickel, 8,%n'~%~r carbon, s' ~ nitrogen,8,,7 and chromium 9 have been varied to d e t e r mine their effect on 7. We are unaware of any m e a surements on c o m m e r c i a l austenitic steels except a few on AISI 304 (Table I). The stacking fault energy of the austenitic (fcc) phase of the F e - C r - N i alloys depends on the exact composition of the steel and generally ranges from 10 to 100 m J / m 2 (1 m J / m z = 1 erg/cm~). Measurements of this p a r a m e t e r reported over the last 17 years are collected in Table I. Various methods for measuring Z have been developed 4 and applied to these materials, q~ne most frequently used method is the measurement of extended dislocation nodes by t r a n s mission electron microscopy. Resolution in the electron microscope r e s t r i c t s this method to cases where ;J ~< 50 m J / m z, except where one m e a s u r e s weak-beam ribbon images. Values reported over the y e a r s are in reasonable agreement with each other when some of the earlier ones are c o r r e c t e d according to Brown's suggestion 23 for an improved theoretical treatment of dislocation line tension. Recently it was shown that the technique of analyzing X - r a y diffraction profiles by
R. E. SCHRAMM is Physicist, and R. P. REED i
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