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Deformation site-specific nature of transgranular carbide precipitation in 304 stainless steels
Scripta METALLURGICA et MATERIALIA
Vol. 28, pp. 1155-1160, 1993 Printed in the U.S.A.
Pergamon Press Ltd. All rights reserved
DEFORMATION SITE-SPECIFIC NATURE OF TRANSGRANULAR CARBIDE PRECIPITATION IN 304 STAINLESS STEELS A.H. Advani, L.E. Murr, D.J. Matlock, W.W. Fisher, P.M. Tarin, C. Ramos, n.J. Romero, R.L. Miller, J.G. Maldonado and C.M. Cedillo Department of Metallurgical and Materials Engineering and Materials Research Institute University of Texas at El Paso, El Paso, TX 79968 (Received June 25, 1992) (Revised February 23, 1993) Introduction Stainless steels (SS) are susceptible to grain boundary carbide precipitation and chromiumdepletion (sensitization) development during thermal treatments typically in the range of 500 850°C (1). Plastic deformation accelerates the development of sensitization in SS, and this acceleration is a function of the amount of strain present in the material and temperature of isothermal treatment (2). Strains above 20% also produce higher amounts of chromium-depletion in SS, though carbide precipitation and depletion occur over both intergranular (IG) and transgranular (TG) regions in the SS (3). The IG and TG chromium-depletion are critical in determining the susceptibility of the alloy to corrosion and stress corrosion cracking (SCC) in boiling water reactor environments, and in SS containers used to store and transport corrosive, toxic and nuclear waste materials (2). Transgranular carbide precipitation and depletion have been studied in some detail in 316 SS in previous work by Advani and Murr (3). Transgranular carbides were observed to form on sitespecific deformation regions in 316 SS. In particular, intersections of microshear bands (which are composed of heterogeneous bundles of twin-faults, and possibly epsilon martensite) were noted to be favored sites for TG carbide formation. This was in agreement with observations made by Weiss and Stickler in 316 SS (4). Transgranular carbide precipitation was also seen to yield significant amounts of TG depletion in the SS, which occurred along slip planes in the material. Briant and Ritter (5,6) investigated TG carbide precipitation and depletion in 304 SS deformed to 5 ksi below the tensile stress of the material. They suggested that TG carbide formation and chromium-depletion in 304 SS was significantly different from 316 SS. This was due to the precipitation of TG carbides on deformation-induced martensite and martensite lath boundaries in 304 SS versus at twin-fault intersections in 316 SS. The carbide precipitation on martensite was also considered to accelerate TG depletion in 304 SS over 316 SS. The relationships between TG carbides, depletion and martensite were, however, not examined in detail, and unambiguous evidence for these relationships was lacking. Other sites for TG precipitation (for example twin-faults and their intersections) were also not evaluated. The objective of the present work was to better understand TG carbide precipitation and depletion in heavily deformed 304 SS. An important goal was to identify the relationship between TG carbides and strain-induced martensite in the material. Since deformation-induced martensite has already been unambiguously identified to nucleate at microshe~r bands in 304 SS, and the crystallography of the martensite nucleation is well understood (7,8), we believed that there may be some subtle alterations in these site-specific nucleation phenomena that could account for both the strain-induced martensite and carbide formation and, thereby, provide a fundamental understanding of carbide precipitation on TG sites in SS. This would yield a better understanding of the mechanisms of (grain boundary) sensitization development, and SCC susceptibility of SS in several aqueous environments.
1155 0956-716X/93 $6.00 + .00 Copyright (c) 1993 Pergamon Press Ltd.
1156
CARBIDE PRECIPITATION
Vol.
28, No. 9
Exoerimental Techniaues The experimental work was carried out on a 6.25 mm thick, high carbon 304 SS plate of composition 0.051%C, 18.29% Cr, 8.22% Ni, 1.47% Mn, 0.025% P, 0.014% S, 0.38% Si, 0.19% Mo, 0.11% Co, 0.19% Cu and 0.085% N. The plate was received in the mill-annealed condition, cut into strips of approximately 125 mm in length x 12 mm width, and solution annealed at 1100°C-1 h for the study. The grain size measured on the material after solution annealing was approximately 175 pm. The strips were deformed in uniaxial tension to a level of ~ 4 0 % true strain ( ~ 4 9 % engineering strain) using a universal tensile testing machine. Samples of 12 mm x 12 mm were then cut from the strips, and heat treated at 670°C for O. 1-10 h to induce TG carbide precipitation and chromium-depletion in the SS. Carbide precipitation in the samples was examined using a Hitachi H-8000 Scanning Transmission Electron Microscope (STEM) operating at 200 kV. Phase identification was carried out using conventional selected area diffraction, microdiffraction and energy dispersive X-ray spectrometry (EDS) techniques. Transgranular chromium-depletion in the materials was examined indirectly using the singleloop version of the electrochemical potentiokinetic reactivation (EPR) test (9). The EPR test measures the charge Q produced during attack of chromium-depletion regions in SS, and normalizes Q with respect to grain boundary area to yield the (grain boundary) sensitization susceptibility of SS. However, our interest was in examination of TG, rather than grain boundary, chromiumdepletion and we had to use optical and scanning electron microscope (SEM) observations of the EPR-attack microstructure as an indicator of the TG depletion in the material (10). Additional details of the TG chromium-depletion evaluation technique and EPR test procedure are given elsewhere (2,9,10). Results and Discussion Deformation was observed to induce significant levels of mixed TG and IG chromiumdepletion in the 40% deformed, 304 SS samples heat treated at 670°C (Figure 1). This is illustrated in optical and SEM micrographs of the EPR-attack microstructure in the 40%-670°C-0.4h samples (Figures l(a) and l(b)). The optical micrograph illustrates the presence of continuous attack on grain boundaries, and significant linear TG attack along slip planes in the material, as has also been noted previously (2-6). This is also reflected in SEM observations illustrating significant grooving of the grain boundary and linearly separated locations of TG attack within grains. Optical analysis, in addition, revealed that some grains had extensive, non-linear, randomized attack within the grain.
Flaur'e 1,
Optical (a) and SEM (b) micrographs illustrating TG and IG attack on 40%-670°C-0.4h EPR-tested samples. Grains with significant levels of linear and non-linear (randomized) TG attack are also indicated in the optical micrograph of (a).
Vol.
28, No.
9
CARBIDE
PRECIPITATION
1157
Transgranular attack in 304 SS occurred due to precipitation of TG carbides within deformed grains in the material. An example of carbide formation within TG regions in 304 SS is illustrated in the bright-field micrograph of Figure 2. The carbides were precipitated on twin-fault intersections in 304 SS, similar to that documented in 316 SS (3,4). It should be noted that the TG carbide illustrated in Figure 2 represents the larger-size carbides, which were observed only after the longest heat treatment of 10h at 670°C. In addition, TG carbide precipitation on twin-fault intersections has been observed to yield linear-TG attack in 316 SS (3,4), as was also seen in this work.
FiQure 2.
Bright-field TEM micrograph illustrating transgranular carbide precipitation at the intersections of twin-faults (T~ and T 2) in 40%-deformed, 670°C-1 Oh treated 304 SS.
Although strain-induced martensite formed at twin-fault intersections in the as-deformed 304 SS (Figure 3), the heat treated materials did not show any strain-induced martensite at these intersections. Detailed microdiffraction analysis of intersections where TG carbides formed, likewise, did not show the presence of any strain-induced martensite in the vicinity of the carbide. The observations suggest that there is a possibility that the strain-induced martensite may be annihilated/transformed during heat treatment, and that there is no correlation between the straininduced martensite and the onset of carbide precipitation in 304 SS, as was described previously (5,6). The differences with the previous work may be due to heat-to-heat variations among stainless steels, differences in cold work conditions studied, or limited area observed during TEM. Our observation of the absence of a correlation between strain-induced martensite and carbides at twin-fault intersections is, however, supported by the fact that TG carbides form at twin-fault intersections in 316 SS, even though no strain-induced martensite forms in 316 SS (2). Instead, with heat treatment, a "new" clustered region was observed to form in the SS as is shown in the bright-field micrograph of Figure 4. Analysis of microdiffraction patterns obtained from the region indicated that it contained martensite and fine-austenite grains. However, the "celllike" appearance of the martensite and its growth outside twin-fault intersections suggested that the phase was not strain-induced martensite, but was more typical of lath martensite. And, although both the lath martensite and strain-induced martensite phases had the same BCC crystal structure and lattice parameter, we believe that the crystallography and mechanisms of the two martensitic transformations would be different. Furthermore, we consider that the lath phase tends to form during the heat treatment process, while the strain-induced martensite forms during (room temperature) straining of the SS under specific conditions described by Olsen and Cohen (8); hence, we regard the lath martensite to be a "thermally" induced, rather than a "strain-induced" martensite. The clustered regions were also observed to form critical sites for TG carbide precipitation in the heat treated SS. While both lath martensite and fine-austenite boundaries were observed
1158
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Fiaure 3.
Bright field and dark field TEM micrographs illustrating the formation of strain-induced martensite at twin-fault intersections (T1 and T2) in as-deformed 304 SS.
Fiaure 4.
Clustered region showing examples of lath martensite (M) and fina-austenite grains (A) in deformed 304 SS, heat treated at 670°C for 0.4h.
Vol.
28, No.
9
CARBIDE
PRECIPITATION
1159
to be favored sites for carbide precipitation, the example illustration in Figure 5 only shows the precipitation of carbides in a predominantly fine-austenite region in the SS. Lattice images of carbides are seen on several fine-austenite boundaries in the material. Detailed views indicate the presence of dislocations within the carbides and at the carbide-matrix interface, and changes in the carbide lattice orientation across the boundary. These may be indicators of key mechanisms involved in carbide nucleation on grain boundaries in SS. We also believe that carbides tend to form on fine-austenite and lath martensite boundaries because these boundaries will behave similar to "regular" grain boundaries in SS. The precipitation of these random TG carbides in the SS may also be the cause for the extensive, random TG attack alluded to in Figure 1. We will focus our future research on developing a better understanding of the formation of lath (thermal) martensite and fine-austenite during heat treatment of deformed 304 SS and identifi/ing relationships between carbide precipitates and chromium-depletion in the SS.
Spmm•rv and Conclusions This research was developed to identify the nature of TG carbide precipitation and chromiumdepletion in heavily deformed 304 SS, and to examine the correlation between carbide precipitation and strain-induced martensite in the SS. Observations have indicated that: • • • • •
Transgranular carbides form on twin-fault intersections in 304 SS. This causes linear-TG attack within the SS There was no observed correlation between strain-induced martensite and TG carbides in this work, except that both form at micro-shear band intersections, but not at the same intersection. Lath martensite and fine-austenite form during heat treatment of deformed, 304 SS. Transgranular carbides precipitate on martensite lath/fine-austenite boundaries in 304 SS, and produce extensive, random TG attack in the SS. Lattice imaging of carbides has shown the presence of dislocations within the carbides and at the carbide-matrix interface, and changes in the carbide lattice orientation across a boundary, which may be indicators of key mechanisms of carbide nucleation on grain boundaries in SS. Acknowledqements
Funding for this research was obtained from a National Science Foundation (RIMI) Grant HRD 9105065 and Environmental Protection Agency cooperative agreement CR-818296-01-0 through the Southwest Center for Environmental Research and Policy (SCERP). The work was also funded in part by DOD Grant DN-009, Defense Logistics Agency, Directorate of Stockpile Management and General Services Administration Grant PF90-018, administered by the University of Texas at El Paso's Materials Research Institute.
References 1.
2. .
4. 5. 6. 7. 8. 9. 10.
S.M. Bruemmer, Corrosion, 1990, 46, pp.698-709. A.H. Advani, L.E. Murr, D.G. Atteridge and R. Chelakara, Metall. Trans. A, 22A, 1991, pp.2917-2934. A.H. Advani and L.E. Murr, Scripta Metall. et. Mater., 26(2), 1991, pp. 349-353. B. Weiss and R. Stickler, Metall. Trans. A, 3A (1972), p. 851. C.L. Briant and A.M. Ritter, Scripta Metall., 1979, 13, pp. 177-180. C.L. Briant and A.M. Ritter, Metall. Trans. A, 1980, 11A, pp. 2009-2017. L.E. Murr, K.P. Staudhammer, and S.S. Hecker, Metall. Trans. A, 13A, 1982, pp. 627-635. G.B. Olsen and M. Cohen, J. Less Common Met., 28, 1972, pp. 107-118, W.L. Clarke, R.L. Cowan and W.L. Walker, "Comparative Methods for Measuring Degree of Sensitization in Stainless Steels", in Intergranular Corrosion of Stainless Alloys, ASTM STP 656, 1978, pp. 99-132. A.H. Advani, L.E. Murr, D.G. Atteridge, S.M. Bruemmer and R. Chelakara, "Deformation Effects on Transgranular Carbide Precipitation and Depletion in 316 Stainless Steels", Corrosion, 47(12), 1991, pp. 939-947.
Fiqure 5. Illustration of carbide formation in a region containing (predominantly) fine-austenite in 3 0 4 SS. The detailed lattice images of carbides show dislocations within the carbide and on the carbide-matrix interface, and changes in the lattice orientation of the carbide across the fine-austenite boundary.
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Vol. 28, pp. 1155-1160, 1993 Printed in the U.S.A.
Pergamon Press Ltd. All rights reserved
DEFORMATION SITE-SPECIFIC NATURE OF TRANSGRANULAR CARBIDE PRECIPITATION IN 304 STAINLESS STEELS A.H. Advani, L.E. Murr, D.J. Matlock, W.W. Fisher, P.M. Tarin, C. Ramos, n.J. Romero, R.L. Miller, J.G. Maldonado and C.M. Cedillo Department of Metallurgical and Materials Engineering and Materials Research Institute University of Texas at El Paso, El Paso, TX 79968 (Received June 25, 1992) (Revised February 23, 1993) Introduction Stainless steels (SS) are susceptible to grain boundary carbide precipitation and chromiumdepletion (sensitization) development during thermal treatments typically in the range of 500 850°C (1). Plastic deformation accelerates the development of sensitization in SS, and this acceleration is a function of the amount of strain present in the material and temperature of isothermal treatment (2). Strains above 20% also produce higher amounts of chromium-depletion in SS, though carbide precipitation and depletion occur over both intergranular (IG) and transgranular (TG) regions in the SS (3). The IG and TG chromium-depletion are critical in determining the susceptibility of the alloy to corrosion and stress corrosion cracking (SCC) in boiling water reactor environments, and in SS containers used to store and transport corrosive, toxic and nuclear waste materials (2). Transgranular carbide precipitation and depletion have been studied in some detail in 316 SS in previous work by Advani and Murr (3). Transgranular carbides were observed to form on sitespecific deformation regions in 316 SS. In particular, intersections of microshear bands (which are composed of heterogeneous bundles of twin-faults, and possibly epsilon martensite) were noted to be favored sites for TG carbide formation. This was in agreement with observations made by Weiss and Stickler in 316 SS (4). Transgranular carbide precipitation was also seen to yield significant amounts of TG depletion in the SS, which occurred along slip planes in the material. Briant and Ritter (5,6) investigated TG carbide precipitation and depletion in 304 SS deformed to 5 ksi below the tensile stress of the material. They suggested that TG carbide formation and chromium-depletion in 304 SS was significantly different from 316 SS. This was due to the precipitation of TG carbides on deformation-induced martensite and martensite lath boundaries in 304 SS versus at twin-fault intersections in 316 SS. The carbide precipitation on martensite was also considered to accelerate TG depletion in 304 SS over 316 SS. The relationships between TG carbides, depletion and martensite were, however, not examined in detail, and unambiguous evidence for these relationships was lacking. Other sites for TG precipitation (for example twin-faults and their intersections) were also not evaluated. The objective of the present work was to better understand TG carbide precipitation and depletion in heavily deformed 304 SS. An important goal was to identify the relationship between TG carbides and strain-induced martensite in the material. Since deformation-induced martensite has already been unambiguously identified to nucleate at microshe~r bands in 304 SS, and the crystallography of the martensite nucleation is well understood (7,8), we believed that there may be some subtle alterations in these site-specific nucleation phenomena that could account for both the strain-induced martensite and carbide formation and, thereby, provide a fundamental understanding of carbide precipitation on TG sites in SS. This would yield a better understanding of the mechanisms of (grain boundary) sensitization development, and SCC susceptibility of SS in several aqueous environments.
1155 0956-716X/93 $6.00 + .00 Copyright (c) 1993 Pergamon Press Ltd.
1156
CARBIDE PRECIPITATION
Vol.
28, No. 9
Exoerimental Techniaues The experimental work was carried out on a 6.25 mm thick, high carbon 304 SS plate of composition 0.051%C, 18.29% Cr, 8.22% Ni, 1.47% Mn, 0.025% P, 0.014% S, 0.38% Si, 0.19% Mo, 0.11% Co, 0.19% Cu and 0.085% N. The plate was received in the mill-annealed condition, cut into strips of approximately 125 mm in length x 12 mm width, and solution annealed at 1100°C-1 h for the study. The grain size measured on the material after solution annealing was approximately 175 pm. The strips were deformed in uniaxial tension to a level of ~ 4 0 % true strain ( ~ 4 9 % engineering strain) using a universal tensile testing machine. Samples of 12 mm x 12 mm were then cut from the strips, and heat treated at 670°C for O. 1-10 h to induce TG carbide precipitation and chromium-depletion in the SS. Carbide precipitation in the samples was examined using a Hitachi H-8000 Scanning Transmission Electron Microscope (STEM) operating at 200 kV. Phase identification was carried out using conventional selected area diffraction, microdiffraction and energy dispersive X-ray spectrometry (EDS) techniques. Transgranular chromium-depletion in the materials was examined indirectly using the singleloop version of the electrochemical potentiokinetic reactivation (EPR) test (9). The EPR test measures the charge Q produced during attack of chromium-depletion regions in SS, and normalizes Q with respect to grain boundary area to yield the (grain boundary) sensitization susceptibility of SS. However, our interest was in examination of TG, rather than grain boundary, chromiumdepletion and we had to use optical and scanning electron microscope (SEM) observations of the EPR-attack microstructure as an indicator of the TG depletion in the material (10). Additional details of the TG chromium-depletion evaluation technique and EPR test procedure are given elsewhere (2,9,10). Results and Discussion Deformation was observed to induce significant levels of mixed TG and IG chromiumdepletion in the 40% deformed, 304 SS samples heat treated at 670°C (Figure 1). This is illustrated in optical and SEM micrographs of the EPR-attack microstructure in the 40%-670°C-0.4h samples (Figures l(a) and l(b)). The optical micrograph illustrates the presence of continuous attack on grain boundaries, and significant linear TG attack along slip planes in the material, as has also been noted previously (2-6). This is also reflected in SEM observations illustrating significant grooving of the grain boundary and linearly separated locations of TG attack within grains. Optical analysis, in addition, revealed that some grains had extensive, non-linear, randomized attack within the grain.
Flaur'e 1,
Optical (a) and SEM (b) micrographs illustrating TG and IG attack on 40%-670°C-0.4h EPR-tested samples. Grains with significant levels of linear and non-linear (randomized) TG attack are also indicated in the optical micrograph of (a).
Vol.
28, No.
9
CARBIDE
PRECIPITATION
1157
Transgranular attack in 304 SS occurred due to precipitation of TG carbides within deformed grains in the material. An example of carbide formation within TG regions in 304 SS is illustrated in the bright-field micrograph of Figure 2. The carbides were precipitated on twin-fault intersections in 304 SS, similar to that documented in 316 SS (3,4). It should be noted that the TG carbide illustrated in Figure 2 represents the larger-size carbides, which were observed only after the longest heat treatment of 10h at 670°C. In addition, TG carbide precipitation on twin-fault intersections has been observed to yield linear-TG attack in 316 SS (3,4), as was also seen in this work.
FiQure 2.
Bright-field TEM micrograph illustrating transgranular carbide precipitation at the intersections of twin-faults (T~ and T 2) in 40%-deformed, 670°C-1 Oh treated 304 SS.
Although strain-induced martensite formed at twin-fault intersections in the as-deformed 304 SS (Figure 3), the heat treated materials did not show any strain-induced martensite at these intersections. Detailed microdiffraction analysis of intersections where TG carbides formed, likewise, did not show the presence of any strain-induced martensite in the vicinity of the carbide. The observations suggest that there is a possibility that the strain-induced martensite may be annihilated/transformed during heat treatment, and that there is no correlation between the straininduced martensite and the onset of carbide precipitation in 304 SS, as was described previously (5,6). The differences with the previous work may be due to heat-to-heat variations among stainless steels, differences in cold work conditions studied, or limited area observed during TEM. Our observation of the absence of a correlation between strain-induced martensite and carbides at twin-fault intersections is, however, supported by the fact that TG carbides form at twin-fault intersections in 316 SS, even though no strain-induced martensite forms in 316 SS (2). Instead, with heat treatment, a "new" clustered region was observed to form in the SS as is shown in the bright-field micrograph of Figure 4. Analysis of microdiffraction patterns obtained from the region indicated that it contained martensite and fine-austenite grains. However, the "celllike" appearance of the martensite and its growth outside twin-fault intersections suggested that the phase was not strain-induced martensite, but was more typical of lath martensite. And, although both the lath martensite and strain-induced martensite phases had the same BCC crystal structure and lattice parameter, we believe that the crystallography and mechanisms of the two martensitic transformations would be different. Furthermore, we consider that the lath phase tends to form during the heat treatment process, while the strain-induced martensite forms during (room temperature) straining of the SS under specific conditions described by Olsen and Cohen (8); hence, we regard the lath martensite to be a "thermally" induced, rather than a "strain-induced" martensite. The clustered regions were also observed to form critical sites for TG carbide precipitation in the heat treated SS. While both lath martensite and fine-austenite boundaries were observed
1158
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28, No. 9
Fiaure 3.
Bright field and dark field TEM micrographs illustrating the formation of strain-induced martensite at twin-fault intersections (T1 and T2) in as-deformed 304 SS.
Fiaure 4.
Clustered region showing examples of lath martensite (M) and fina-austenite grains (A) in deformed 304 SS, heat treated at 670°C for 0.4h.
Vol.
28, No.
9
CARBIDE
PRECIPITATION
1159
to be favored sites for carbide precipitation, the example illustration in Figure 5 only shows the precipitation of carbides in a predominantly fine-austenite region in the SS. Lattice images of carbides are seen on several fine-austenite boundaries in the material. Detailed views indicate the presence of dislocations within the carbides and at the carbide-matrix interface, and changes in the carbide lattice orientation across the boundary. These may be indicators of key mechanisms involved in carbide nucleation on grain boundaries in SS. We also believe that carbides tend to form on fine-austenite and lath martensite boundaries because these boundaries will behave similar to "regular" grain boundaries in SS. The precipitation of these random TG carbides in the SS may also be the cause for the extensive, random TG attack alluded to in Figure 1. We will focus our future research on developing a better understanding of the formation of lath (thermal) martensite and fine-austenite during heat treatment of deformed 304 SS and identifi/ing relationships between carbide precipitates and chromium-depletion in the SS.
Spmm•rv and Conclusions This research was developed to identify the nature of TG carbide precipitation and chromiumdepletion in heavily deformed 304 SS, and to examine the correlation between carbide precipitation and strain-induced martensite in the SS. Observations have indicated that: • • • • •
Transgranular carbides form on twin-fault intersections in 304 SS. This causes linear-TG attack within the SS There was no observed correlation between strain-induced martensite and TG carbides in this work, except that both form at micro-shear band intersections, but not at the same intersection. Lath martensite and fine-austenite form during heat treatment of deformed, 304 SS. Transgranular carbides precipitate on martensite lath/fine-austenite boundaries in 304 SS, and produce extensive, random TG attack in the SS. Lattice imaging of carbides has shown the presence of dislocations within the carbides and at the carbide-matrix interface, and changes in the carbide lattice orientation across a boundary, which may be indicators of key mechanisms of carbide nucleation on grain boundaries in SS. Acknowledqements
Funding for this research was obtained from a National Science Foundation (RIMI) Grant HRD 9105065 and Environmental Protection Agency cooperative agreement CR-818296-01-0 through the Southwest Center for Environmental Research and Policy (SCERP). The work was also funded in part by DOD Grant DN-009, Defense Logistics Agency, Directorate of Stockpile Management and General Services Administration Grant PF90-018, administered by the University of Texas at El Paso's Materials Research Institute.
References 1.
2. .
4. 5. 6. 7. 8. 9. 10.
S.M. Bruemmer, Corrosion, 1990, 46, pp.698-709. A.H. Advani, L.E. Murr, D.G. Atteridge and R. Chelakara, Metall. Trans. A, 22A, 1991, pp.2917-2934. A.H. Advani and L.E. Murr, Scripta Metall. et. Mater., 26(2), 1991, pp. 349-353. B. Weiss and R. Stickler, Metall. Trans. A, 3A (1972), p. 851. C.L. Briant and A.M. Ritter, Scripta Metall., 1979, 13, pp. 177-180. C.L. Briant and A.M. Ritter, Metall. Trans. A, 1980, 11A, pp. 2009-2017. L.E. Murr, K.P. Staudhammer, and S.S. Hecker, Metall. Trans. A, 13A, 1982, pp. 627-635. G.B. Olsen and M. Cohen, J. Less Common Met., 28, 1972, pp. 107-118, W.L. Clarke, R.L. Cowan and W.L. Walker, "Comparative Methods for Measuring Degree of Sensitization in Stainless Steels", in Intergranular Corrosion of Stainless Alloys, ASTM STP 656, 1978, pp. 99-132. A.H. Advani, L.E. Murr, D.G. Atteridge, S.M. Bruemmer and R. Chelakara, "Deformation Effects on Transgranular Carbide Precipitation and Depletion in 316 Stainless Steels", Corrosion, 47(12), 1991, pp. 939-947.
Fiqure 5. Illustration of carbide formation in a region containing (predominantly) fine-austenite in 3 0 4 SS. The detailed lattice images of carbides show dislocations within the carbide and on the carbide-matrix interface, and changes in the lattice orientation of the carbide across the fine-austenite boundary.
Z o
oo
o k-=
0 Z
po
po tz~
('3
0