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    duplex artigo duplex artigo Document Transcript

    • APFIM and AEM investigation of CF8 and CF8M pril11ary coolant pipe steels Atom probe field ion microscopy, analytical electron microscopy, and optical microscopy have been used to investigate the changes that occur in the microstructure of cast CF8 and CF8M primary coolant pipe steels after long term thermal aging. These cast steels have a duplex microstructure consisting of austenite with approximately 15 vol. -% ferrite. In material aged at 300 or 400°C for up to 70 000 h, the ferrite had spinodally decomposed into a modulated fine scale interconnected network consisting of an iron rich a phase and a chromium enriched a' phase with a periodicity of between 2 and 9 nm. Roughly spherical G phase precipitates 2 to 10 nm in diameter were also observed at concentrations of more than 1021 m-3• The degradation in mechanical properties of these materials is a consequence of the spinodal decomposition and G phase precipitation in the ferrite. MST /1184 M. K. Miller © 1990 The Institute of Metals. The authors are in the Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA. Published by Maney Publishing (c) IOM Communications Ltd J. Bentley Introduction The long term mechanical integrity of pipes used to carry the primary cooling water in pressurised water nuclear reactors is of the utmost importance for safe operation. The coolant pipes are designed for a service life of 40 years. However, it is well known that the mechanical properties of the cast stainless steel pipes that are used for this application are degraded by aging at temperatures in the range 300-400°C. The pipes and other related components are fabricated from stainless steel to reduce corrosion and associated problems at the service temperature of 300°C. These coolant pipes are up to 1 m in diameter and 100 mm thick and, because of their large size, are made by welding cast sections. The type of cast stainless steel that is used has a duplex microstructure of austenite with approximately 1520 vol.-% ferrite. The ferrite is a necessary component of these steels since it improves the properties of the pipes by increasing the yield strength of the cast material and by reducing the susceptibility to hot cracking during solidification. However, long term thermal aging produces an increase in hardness and tensile properties, together with a decrease in the impact properties, ductility, and toughness. Although an in-service failure that is controlled by the impact properties is considered unlikely, these materials can suffer a dramatic loss in impact properties, decreasing to almost 15% of the initial value after prolonged aging. 1 Some microstructural characterisations of several heats of CF8 and other similar steels have been presented.I-3 In these materials, the ferrite decomposes into an iron rich a phase and a chromium enriched a' phase. In addition, a .complex nickel silicide known as G phase is observed in the ferrite. These fine scale phase transformations are considered to be responsible for the degradation in mechaniCal properties. In come cases, M23C6 carbide formation occurs at the ferrite/austenite interface. In this paper a review is presented of a combined atom. probe field ion microscopy (APFIM) and analytical electron microscopy (AEM) study that was performed to Table 1 Nominal bulk composition of CF8 and CF8M steels, wt·% C Si Mn S Cr Mo 1·0 0·28 0·019 20·2 0·13 0·81 0·79 0·021 20·8 2·5 N Fe 8·3 0·027 10·6 0·042 Sal. Experimental The nominal compositions of the CF8 (heat 278 from Georg Fischer Co., Switzerland) and the CF8M alloys used in this investigation are given in Table 1. The major difference between these two materials is that the CF8M alloy has higher molybdenum and nickel levels than the CF8 steel. The CF8M steel was examined in the as cast, unaged condition and also after aging for 7500 h at 400°C, whereas the CFS steel was examined after laboratory aging cast material for 70 000 hat 300,350, and 400°C. It should be noted that the 400°C aging temperature is approximately 100 K higher than the normal service temperature and was used to accelerate the microstructural changes that may occur during service.14 Since these pipes are external to the reactor they are not exposed to any significant levels of radiation that may influence the aging behaviour. Atom probe analyses were conducted primarily on the ORNL * energy compensated atom probe, 15 although initial experiments on the CF8M steel were performed on the straight time of flight atom probe at the University of Oxford. Details of these instruments and the types of analysis that may be performed are described elsewhere. 16, 7 1 Field ion micrographs (FIM) were recorded using neon as the image gas and a specimen temperature between 70 and 90 K. Atom probe composition profiles were analysed using a variety of statistical techniques including: chi-squared frequency distribution tests,17 autocorrelation functions,17 Johnson and Klotz Markov chain analysis, 17,18 Hetherington and Miller mean separation method, 17,19nd a the sample distribution analysis methodll-13 developed by the atom probe group at the University of Oxford. For the frequency distribution tests, the autocorrelation analysis, and the sample distribution analysis, the atom probe data were divided in blocks each containing 50 ions and their composition determined. The standard chi-squared test of the frequency distribution examines whether the observed Sal. Ni CF8 0·038 characterise and compare the microstructures of cast CF8 and CF8M stainless steels and to determine the changes that occur during long term, low temperature thermal aging.4-10These types of steel have also been studied using the atom probe by Godfrey and co-workers.ll-13 CF8M 0·04 * Oak Ridge National Laboratory. Materials Science and Technology March 1990 Vol. 6 285
    • 286 Miller and Bentley APFIM and AEM of CF8 and CF8M primary coolant pipe steels Published by Maney Publishing (c) IOM Communications Ltd a a b 1 b Duplex microstructure in CF8 steel aged for 70000 h at a 300°C and b 400°C: reversion of ferrite and carbide precipitation is evident in material aged at 400°C (TEM) a weak beam TEM of M23C6 particle located at original ferrite/austenite interface; b field ion micrograph (FIM) of brightly imaging M23C6 carbide and ferrite (arrows indicate interface between M23C6 particle and ferrite) 2 distribution of these composition blocks differs from the binomial distribution associated with a random solid solution. The autocorrelation function examines pairs of composition blocks a fixed distance or lag apart and sums the results over the entire composition profile. If the compositions of these blocks deviate from the mean composition in the same sense then a positive correlation is determined. The autocorrelation of adjacent composition blocks in the profile'l provides a technique to detect phase separation or clustering. The sample distribution analysis attempts to quantify the extent of phase separation by calculating the compositional range 2Pa of the observed distribution.ll-13 Both the Johnson and Klotz and the Hetherington and Miller methods examine the atom-by-atom data chain in order to detect phase separation or measure the extent of clustering. The Johnson and Klotz method determines an ordering parameter ()from the number of AA, AB, and BB pairs of atoms in the data chain and compares the result with that expected from a random solid solution.I7,18 The Hetherington and Miller mean separation method compares the variance of the distances between similar type atoms in the data chain with that expected from a random distribution. 17, 19 Materials Science and Technology March 1990 Vol. 6 Carbide precipitates in CF8 steel aged for 70 000 h at 400°C Analyses using AEM were performed on Philips EM400T /PEG and EM430T analytical electron microscopes both equipped with EDAX 9100/70 energy dispersive X-ray spectrometers (EDS) and Gatan 607 electron energy loss spectrometer (EELS) systems. The elemental compositions were obtained from EDS data by standardless procedures. It should be noted that the chromium contents are probably 1-2% overestimated because offluorescence effects and these compositions are averages of the microstructure, including any decomposition that had occurred. This is particularly relevant in the ferrite as shown below. Results GENERAL MICROSTRUCTURE Optical microscopy indicated that the cast and aged materials consisted of a duplex microstructure of austenite with approximately 15% 0 ferrite. Analyses of the compos-
    • Miller and Bentley Published by Maney Publishing (c) IOM Communications Ltd 3 Austenite and ferrite 400°C (TEM)) APFIM and AEM of CF8 and CF8M primary of austenite of compositions EDS analysis ferrite, wt-% pipe steels 287 in CF8M steel aged for 7500 h at itions of the ferrite and austenite by EDS in the unaged CF8M material revealed that the ferrite was enriched in chromium, silicon, and molybdenum and depleted in nickel and manganese as can be seen in Table 2. Similar trends were obtained in the CF8 material after the extended aging treatment at 400°C (see Table 2). A comparison of the duplex microstructure of CF8 materials aged at 300 and 400°C is shown in the transmission electron micrographs (TEM) in Fig. 1. In material aged for 70000 h at 400°C, the ferrite had undergone a small amount of reversion to austenite at the ferrite/austenite interface, to a depth of approximately 4 ~m, with the precipitation of some carbides (Fig. 1b). Most of these precipitates were preferentially located at the original ferrite/austenite interface (Fig. 2a). These precipitates imaged brightly in the field ion micrographs as shown in Fig. 2b. No marked reversion was observed in the CF8M material (Fig. 3), but the aging time was an order of magnitude shorter. Electron diffraction and analyses by EDS and EELS revealed that the precipitates were chromium rich M23C6carbides. Atom probe selected area analyses also confirmed that these precipitates were alloy carbides. By contrast, no carbides or reversion of the ferrite were observed in the CF8 alloy aged for 70 000 h at 300°C (Fig. 1a) .. The ferrite had slightly reverted in the CF8 material aged for 70000 h at 350°C, but no carbides were observed at the ferrite/austenite interface. Unfortunately, no material aged at 300°C was available heat treated to the same 'equivalent time'3 as the 400°C aging treatment, so it was not possible to ascertain whether reversion eventually occurs at much longer aging times at 300°C. Aging produced a change in the relative microhardness of the austenite and ferrite phases. The hardness of the ferrite increased significantly, whereas the hardness of the austenite remained essentially constant. Transmission electron micrographs revealed that dislocations in the ferrite in the CF8 steel aged at 300 and 400°C were pinned as shown in Fig. 4. Table 2 coolant and Phase Cr Ni Mn Mo Si Fe CF8M unaged Austenite Ferrite 20·8 26·7 11·4 6·4 1·1 0·8 1·8 4·8 0·8 1·0 Sal. Sal. 0·22 0·08 0·26 0·36 0·99 1·42 Sal. Sal. CF8 aged for 70000 h at 400°C 20·2 8·4 Austenite 28·6 3·7 Ferrite a 4 b Pinned dislocations in ferrite phase in CF8 steel aged for 70 000 h at a 300°C and b 400°C (TEM) Any conclusions based on results of accelerated tests that are performed at 400°C should be carefully examined, since the microstructure that develops is distinctly different from that at 300°C. This difference in the microstructure was indicated by the reversion of the ferrite into austenite and the precipitation of M23C6that occurred at 400°C, 14 but not at the lower temperatures of 350 or 300°C. The presence of these carbides could be a factor in the fracture process and thereby influence the mechanical properties. G PHASE PRECIPITATES Two marked changes in the microstructure and microchemistry of the ferrite were found to accompany low temperature aging in both alloys. Numerous small, roughly spherical precipitates 10 nm in diameter which exhibited brightly imaging contrast in the field ion micrographs (e.g. Fig. 5a) were found distributed throughout the ferrite phase in the CF8M alloy. These precipitates were not observed in field ion micrographs of the austenite (Fig. 5b). The bright spots in the field ion micrograph of austenite are probably due to the presence of molybdenum and silicon and are typical for micrographs of austenite containing large amounts of solute. Precipitates that imaged similarly Materials Science and Technology March 1990 Vol. 6
    • Published by Maney Publishing (c) IOM Communications Ltd 288 Miller and Bentley APFIM and AEM of CF8 and CF8M primary coolant pipe steels a a b b a ferrite with brightly imaging G phase precipitates; 5 b austenite CF8M steel aged for 7500 h at 400°C (FIM) to those in the aged CF8M steel were also observed in the ferrite of the CF8 steel aged at 300 and 400°C, as shown in Fig. 6. The size (1-1·5 nm) and number density (,....., 23 m-3) of these precipitates was approximately similar 10 for the two aging conditions with a slightly larger size and a lower number density for the 400°C aging treatment. Some variation in the distribution of these precipitates was observed from one region of the ferrite to another. The size of these precipitates was smaller than observed in the CF8M steel. The precipitates in the ferrite were also imaged using TEM. A precipitate dark field image is shown in Fig. 7 in the aged CF8M steel, where the precipitates were of uniform size, ,.....,10 in diameter, and were present at a nm number density of ,....., 23 m -3 giving a volume fraction of 10 ,....., in the ferrite. These results are in agreement with the 10% field ion microscopy .observations. However, in CF8 material aged at 300 or 400°C, distinct bimodal size distributions of the precipitates were observed in the TEM (Fig. 8). The smaller precipitates were randomly distributed in the ferrite matrix, whereas the larger precipitates were associated with dislocations (see Fig. 9). The TEM revealed that the finer precipitates were approximately 1·5 and 2 nm in Materials Science and Technology March 1990 Vol. 6 6 Ferrite of CF8 steel aged for 70 000 h at (FIM) a 300°C and b 400°C diameter, and present at number densities of >1024 and ,....., 21 m-3 in the CF8 materials aged at 300 and 400°C, 10 respectively. The discrepancy in the size and number density measured in the FIM and the TEM is a consequence of the small size of the precipitates, since the TEM is not sensitive to the smallest precipitates which results in an underestimation of the number density .and an overestimation of the size. This also illustrates the difficulty in resolving and measuring the extent of precipitates when their size approaches unit cell dimensions. The precipitates were 4 to 5 times larger on the dislocations than in the matrix, presumably as a result of enhanced nucleation and growth because of assistance of pipe diffusion along the dislocation core. G phase precipitates were not observed in the as cast, un aged material or in the austenite in the aged material. Atom probe analysis and EDS analysis of extraction replicas revealed that the precipitates in the aged CF8M ferrite were alloy silicides as shown in Table 3. Selected area electron diffraction patterns of these silicide precipitates (Fig. 7b), were consistent with a fcc crystal structure with some additional features. Lattice parameters of 1·09 and 1·11 nm were measured for the precipitates in the
    • Miller and Bentley APFIM and AEM of CF8 and CF8M primary Table 3 coolant pipe steels 289 APFIM and EDS analysis of composition of G phase precipitates in CF8M steel aged for 7500 h at 400°C, at.-% Si Ni Fe Mo Cr 13·0 ± 2·5 12·0 ± 2·5 1·0 ± 0·7 C APFIM 27·7 ± 3·4 24·0 ± 3·2 20·6 ± 3·1 EDS 20·9 ± 2·0 31·1±2·2 10·5 ± 1·5 19·9 ± 1·1 17·8 ± 2·1 ND ND not detected. phase. The composition, the fcc crystal structure with the weak or absent 220 and 400 and strong 333 reflections in the electron diffraction patterns, the cube on cube orientation relationship with the ferrite matrix, and the lattice parameter all support this identification. G phase is regarded as a complex silicide with a fcc crystal structure containing 116 atoms per unit cell. The model of G phase is based on Ni16ShTi6 with various elements such as Cr, Fe, Mo, Mn, V, Nb, Ta, Hf, and Zr substituting for the titanium and nicke1.20,21 This substitution results in a series of G phases with variable composition and lattice parameter. It should be emphasised that without the characterisation of the CF8M steel, the G phase in the CF8 alloy could have been overlooked because of its small size and weak contribution " to the diffraction patterns. Published by Maney Publishing (c) IOM Communications Ltd a SPINODAL DECOMPOSITION b a dark field TEM; b electron diffraction pattern 7 G phase precipitates in ferrite of CF8M steel after aging for 7500 h at 400°C CF8M and CF8 alloys, respectively. The diffraction patterns also revealed that the precipitates had a cube on cube orientation relationship with the ferrite matrix. These small silicide precipitates in the ferrite phase were identified as G a 8 More detailed analyses of the ferrite matrix in the CF8 steel by AEM and APFIM revealed that it had decomposed during thermal aging. Phase contrast, electron micrographs of the structure in material aged at 300 and 400°C are shown in Fig. lOa, b. The scale of this two phase modulated microstructure was measured frqm these electron micrographs as 4 and 9 nm in the 300 and 400°C aged materials, respectively. A field ion micrograph of the same two phase microstructure in the material aged at 400°C is shown in Fig. 10c, b Bimodal distribution of G phase precipitates in ferrite of CF8 steel aged at a 300°C and h, C 400°C (TEM) Materials Science and Technology March 1990 Vol. 6
    • Published by Maney Publishing (c) IOM Communications Ltd 290 Miller and Bentley APFIM and AEM of CF8 and CF8M primary coolant pipe steels abc a 333 precipitate-reflection dark field TEM; b weak beam, dark field TEM; c superposition of a and b 9 Coarser G phase precipitates associated with dislocations c a, b TEM; c FIM showing brightly imaging a and darkly imaging a' phases 10 Spinodal decomposition into a and a' phases of CF8 steel aged at a 300°C and b, C 400°C Materials Science and Technology March 1990 Vol. 6 of CF8 steel aged at 400°C where the darkly imaging a' and the brightly imaging a phases are evident. The periodicity of the modulations of the two phases was measured from FIM micrographs to be 7 nm. Field evaporation sequences revealed that the modulated microstructure was interconnected, indicative of phase separation by isotropic spinodal decomposition. Atom probe composition profiles through the ferrite also indicated that the ferrite had decomposed into a chromium enriched a' phase and an iron rich a phase. A short section of an atom probe composition profile through the ferrite of the CF8 steel aged for 70 000 h at 400°C is shown in Fig. 11. The large amplitude fluctuations that are evident is indicative of phase separation on a fine scale. Extended composition profiles for both austenite and ferrite phases in the CF8 material were subjected to statistical analyses. The results of these analyses are summarised in Table 4. The sample distribution analysis, autocorrelation function rb the Johnson and Klotz (JK) Markov chain ordering parameter (), and the Hetherington and Miller mean separation method all indicated that the ferrite had phase separated into iron rich and chromium enriched regions and the chisquared tests of the frequency distributions indicate that the solute was not randomly distributed. With the exception of the Pa sample distribution analysis, the statistical analysis of the austenite indicated a random distribution of chromium. The significance of Pa was much smaller for the austenite (3·1) than for the ferrite (22). Atom probe composition profiles were obtained from the ferrite phase in the CF8M steel, avoiding the silicide precipitates, and also revealed decomposition into the a and a' phases, as shown in Fig. 12 The absolute compositions of the two phases are probably more extreme than those indicated from the composition profile, since the probe aperture was larger than the extent of the chromium enriched regions and therefore some averaging of the composition of the two phases occurred. The phase separation was not resolved in the field ion micrographs, partly because of the extremely fine scale (,.....2 nm) and partly because the silicide precipitates altered the local imaging conditions.
    • Miller and Bentley APFIM and AEM of CF8 and CF8M primary 70 coolant pipe steels 291 60 AGED 70 OOOh AT 400°C 60 AGED 7500h AT 4000C 50 50 ?fl ~ ~40 :E 2 30 :E 0 0:: ::r: u 20 ~ ~30 I 0 20 10 10 0 Published by Maney Publishing (c) IOM Communications Ltd 11 40 o 100 200 300 DISTANCE - 50 ION BLOCKS Section of atom probe composition profile through ferrite phase of CF8 steel aged for 70 000 h at 400°C showing phase separation into iron rich a and chromium enriched a' phases Discussion The microstructures of the CF8 and CF8M steels were similar. In both types of steel the ferrite spino dally decomposed into an isotropic network of a and a' phases and G phase precipitates. The major difference between the two types of steel was the size and volume fraction of the G phase precipitates. In the CF8M material aged for 7500 hat 400°C, the G phase precipitates exhibited a much larger volume fraction compared with the CF8 steel that was also aged at 400°C, but for almost 10 times longer. This larger volume of G phase is related to the differences in initial composition between the two alloys. The G phase silicide is rich in nickel and molybdenum which were present at higher levels in the CF8M steel than in the CF8 steel. Although a small fraction of the G phase precipitates was observed pinning dislocations, it should be noted that these residual dislocations will not be of the same type, or behave in the similar manner, as those generated during further deformation. G phase precipitates on dislocations in ferrite have also been observed by Vitek22 in similar steels. A reduction in the levels of silicon, nickel, and perhaps molybdenum in the ferrite would reduce or even suppress the amount of G phase that is precipitated. The composition of the ferrite phase is in the range where a miscibility gap exists at low temperatures. Phase separation of the ferrite into a chromium enriched phase and an iron rich phase is similar to that observed in Fe-Cr and many Fe-Cr-X systems which undergo isotropic spinodal decomposition within a miscibility gap under certain conditions. Relatively small changes in the chromium and molybdenum levels in the ferrite will alter the position in the miscibility gap and therefore the volume fraction of the iron rich and chromium enriched phases. This could affect the morphology of the transformation products and hence alter the mechanical properties and aging behaviour. However, Table 4 Summary 400°C of statistical 5 6 7 Atom probe composition profile in ferrite phase of aged CF8M steel showing phase separation into iron rich a and chromium enriched a' phases changing the chromium content of the alloy does not necessarily change the composition of the ferrite; it may merely alter the quantity of ferrite. The fine scale spinodal decomposition and the G phase precipitation in the ferrite bo~h contribute to the changes in mechanical properties that occur during aging. However, since the volume of G phase was much lower in the CF8 than in· the CF8M steel and the behaviour of the steels is similar, the degradation in mechanical properties is primarily due to the spinodal decomposition of the ferrite during aging. In addition, the observation that the increase in hardness in the CF8 and CF8M steels is similar to that previously observed in a spino dally decomposed Fe-30Cr alloy which did not contain G phase,23 also suggests that spinodal decomposition is the primary factor influencing mechanical properties. The results presented here are specific to the material and heat treatment and may vary considerably in each individual casting depending on the precise alloy composition and casting conditions. Conclusions The results of this study have pointed out the complexity and the very fine scale of the decomposition processes that occur at low temperatures in CF8 and CF8M type stainless steels. This study has also shown that the near atomic resolution of the atom probe was able to detect and quantify the extremely fine scale phase separation that occurred. Both APFIM and AEM results indicate that the chromium enriched ferrite had decomposed into a very fine network of chromium enriched a' and iron rich a phases as a result of isotropic spinodal decomposition. Coarse M23C6 precipitates were observed at the ferrite/austenite interface in the CF8 steel aged at 400°C. Very fine G phase silicide precipitates were observed in the ferrite. A comparison between the results from the CF8 and CF8M steels indicates that J and K Markov chain Autocorrelation function Phase Pa r, () Ferrite Austenite 0·066 ± 0·003 0·028 ± 0·009 0·467 ± 0·06 0·24 ± 0·09 1·129 1·011 DF degrees 12 3 4 DISTANCE (nm) analysis of atom probe data for CF8 stainless steel aged for 70 000 h at Sample distribution analysis Sig. significance; 2 Frequency distribution Sig. Mean separation Sig. X2 DF 4·26 0·34 6·35 1·65 43·0 19·1 22 13 of freedom. Materials Science and Technology March 1990 Vol. 6
    • 292 Miller and Bentley APFIM and AEM of CF8 and CF8M primary coolant pipe steels relatively small differences in the alloy compositions significantly alter the quantity of G phase present in the microstructure. The degradation in mechanical properties is a consequence of the spinodal decomposition of the ferrite together with G phase precipitation that occurs during aging. Published by Maney Publishing (c) IOM Communications Ltd Acknowledgments This research was sponsored by the Division of Materials Sciences, US Department of Energy, under contract DE-AC05-840R21400 with Martin Marietta Energy Systems, Inc. The authors would like to thank Dr H. M. Chung and Dr O. K. Chopra of Argonne National Laboratory for supplying the aged CF8 steels, Dr J. A. Spitznagel of Westinghouse R&D Center, Pittsburgh, PA, for supplying the CF8M alloy, Dr M. G. Hetherington of the University of Oxford for providing the sample distribution software, Dr G. D. W. Smith of the University of Oxford for use of the atom probe for some of the analyses, and Ms K. F. Russell for her technical assistance. References 1. o. K CHOPRAand H. M. CHUNG:in Proc. 13th Water Reactor Safety Research Information Meeting, 1985, Gaithersburg, MD, US National Bureau of Standards. 2. H. M. CHUNGand o. K. CHOPRA:in Proc. 2nd Int. Symp. on 'Environmental degradation of materials in nuclear power systems - water reactors, (ed. J. T. Roberts et al.), 287-292; 1985, Monterey, CA, American Nuclear Society. 3. H. M. CHUNGand o. K. CHOPRA:Properties of stainless steels in ' elevated temperature service', (ed. M. Prager), PVP-ASME Vol. 132, MPC Vol. 26, 17-34; 1987, New York, ASMEjMaterials Properties Council. 4. M. K. MILLER,J. BENTLEY, . s. BRENNER, nd J. A. SPITZNAGEL: S a J. Phys., 1984, 45-C9, 385-390. 5. M. K. MILLERand 1. BENTLEY: . Phys., 1986, 47-C7, 239-244. J 6. M. K. MILLER,1. BENTLEY, . s. BRENNER, nd 1. A. SPITZNAGEL: S a in Proc. 43rd Annual Meeting of the Electron Microscopy Society of America, (ed. G. W. Bailey), 326-327; 1985, San Francisco, San Francisco Press. 7. 1. BENTLEY, . K. MILLER,S. S. BRENNER, nd 1. A. SPITZNAGEL: M a in Proc. 43rd. Annual Meeting of the Electron Microscopy Society of America, (ed. G. W. Bailey), 328-329; 1985, San Francisco, San Francisco Press. 8. 1. BENTLEY and M. K. MILLER:in 'Analytical electron microscopy', (ed. D. C. Joy), 73-75; 1987, San Francisco, San Francisco Press. . 9. M. K. MILLERand 1. BENTLEY:in Proc. 3rd Int. Symp. on 'Environmental degradation of materials in nuclear power systems - water reactors, (eds. G. J. Theus and J. R. Weeks), 341-349; 1988, Pittsburgh, PA, TMS. 10. 1. BENTLEY M. K. MILLER:in MRS Symp. 'Characterization and of defects in materials', Vol. 82, (eds. R. W. Siegeletal.), 163168; 1987, Pittsburgh, PA, Materials Research Society. 11. T. J. GODFREY G. D. W. SMITH:J. Phys., 1986, 47-C7, 217and 222. 12. T.1. GODFREY, . G. HETHERINGTON, M. SASSEN,and G. D. W. M 1. SMITH:J. Phys., 1988, 49-C6, 421-426. 13. 1. M. SASSEN,M. G. HETHERINGTON, 1. GODFREY, D. W. SMITH, T. G. P. H. PUMPHREY, nd K. N. AKHURST:n 'Properties of stainless a i steels in elevated temperature service', (ed. M. Prager), PVPASME Vol. 132, MPC Vol. 26, 65-78; 1987, New York, ASMEjMaterials Properties Council. 14. G. SLAMA, P. PETREQUIN,S. H. MASSON, and T. MAGER:in Structural Mechanics in Reactor Technology (SMIRT) Postconference Seminar 6, 'Assuring structural integrity of steel reactor pressure boundary components', Monterey, CA, August 1983. 15. M. K. MILLER:J. Phys., 1986, 47-C2, 493-498 and 499-504. 16. M. K. MILLER:Int. Mater. Rev., 1987,32,221-240. 17. M. K. MILLERand G. D. W. SMITH:'Atom probe microanalysis: principles and applications to materials problems'; 1989, Pittsburgh, P A, Materials Research Society. 18. c. A. JOHNSONand 1. H. KLOTZ:Teehnometries, 1974, 16, 483493. 19. M. G. HETHERINGTONnd M. K. MILLER:J. Phys., 1987, 48-C6, a 559-561. 20. F. X. SPIEGEL,D. BARDOS,and P. A. BECK:Trans, AIME, 1963, 227, 575. . 21. E. H. LEE, P. 1. MAZIASZ,andA. F. ROWCLIFFE: 'Phase stability in during irradiation', (ed. J. R. Holland et. al.), 191-218; 1981, Warrendale, PA, The Metallurgical Society of AIME. 22. 1. M. VITEK:Metall. Trans., 1987, 18A, 154-156. 23. s. S. BRENNER, . K. MILLER,and w. A. SOFFA:Ser. Metall., 1982, M 16, 831-836. IRONMAKING AND STEELMAKING (alternate-monthly) Provides international coverage of all aspects of iron and steelmaking, including the rolling and application of ferrous products. 1990 Subscription Rates: £95.00 US$225.00 Members: £54.00 US$108.00 Orders with remittance to: The Institute of Metals, Sales & Marketing Dept., 1 Carlton House Terrace, London SW1Y 5DB. Tel. 071-976 1338 Fax. 071-839 2078 Materials Science and Technology March 1990 Vol. 6