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TitleEnvironmentally Assisted Cracking in Light Water Reactors
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NUREG/CR-4667, Vol. 32

Environmentally Assisted
Cracking in
Light Water Reactors

Annual Report
January - December 2001

Argonne National Laboratory

U.S. Nuclear Regulatory Commission
Office of Nuclear Regulatory Research
Washington, DC 20555-0001

Page 2


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Page 41

presence of delta ferrite globules and austenite ferrite phase boundaries. As a consequence,
the oncentration of S on austenite grain boundaries is expected to be low, and the
susceptibility to'IASCC (i.e., IGSCC along austenite grain boundaries) is suppressed in
irrad iated steels that contain delta ferrite even in small volume fraction. If the volume fraction
of delta ferrite is too large, however, signficant embrittlement of the ferrite phase could lead to
unacceptable degrdation of the fracture toughness of irradiated steel. Explanation based on
this model needs, 'however, to be confirmed by further investigations, e.g., AES analysis of S on
grain boundaries and quantitative metallography of.ferrite and MnS inclusions.


0 n* deft 0. (Lxlnii 4n
ea 25° -*.OXlO"nn 4m - Figure 19.

60 - - .- l; D | " 2.0xa0ana -Effects of delta ferrite on susceptibility to
co Q -QQ15K*S IASCC, as reflected in IGSCC data, of

no* I dor heats that contain high concentrations of
8 40 - sulfur. Note that Heat-L5, which contains

-3 vol.% ferrite, is resistant to IASCC but
20 Heats C9 and L18 that contain no delta

:_ Clue WL%ferrite are highly susceptible to IASCC.
dglt fy3 ol.%

ce L42 LS

Figure 20.
Optical photomicrograph of

IAC-resistat high-Cr Alloy
L5 (21 wt.% Cr), showing twins

t a~~ind 3- to 15-prrn-diameter
globules of delta ferrite.

1600 .;
1534 L

8 + L

1400 1365'

1300 /\Figure 21.
1300 _y 0.06 W t% 0.18 Fe-rich side of Fe-S phase diagram,

from M. Hansen, Constitution of
L 1200 + Binary Alloys," McGraw Hill,
E y + LJNew York, NY, 1958, pp. 704-707.


Page 42

Figure 22 shows a predominantly intergranular-fracture surface morphology in Type 304
SS Heats C9 and L18 that contain high concentrations of S and were irradiated to =3 dpa
(Fig. 19). The figure also shows a predominantly ductile-dimple fracture surface morphology in
Alloy L5 that contains high concentrations of S and =3 vol.% S ferrite.


Figure 22.
Fracture surface morphology of IASCC-
susceptible high-S Heats (a) C9 (0.013 wt.% S)
and (b) LI 8 (0.033 wt.% S), and (c) IASCC-
resistant Alloy L5 that contains high concentration
of S (0.028 wt.% S) and =3 vol.% ferrite. All
specimens were irradiated to =2 x 1021 n cm-2
(=3 dpa).




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Federal Recycling Program

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