ASTM A763-93(2004)
(Practice)Standard Practices for Detecting Susceptibility to Intergranular Attack in Ferritic Stainless Steels
Standard Practices for Detecting Susceptibility to Intergranular Attack in Ferritic Stainless Steels
ABSTRACT
This practices covers the detecting susceptibility to intergranular attack in ferritic stainless steel. Different method of preparing steel test specimens are presented. Four practices, including Practice W, X, Y, and Z, are used for determining susceptibility to intergranular attack in ferritic stainless steel. These practices cover the following tests; oxalic acid etch test, ferritic sulphate-sulfuric acid test, copper-copper sulphate-50% sulfuric acid test, and copper-copper sulphate-16% sulfuric acid test. Test specimens shall be examined for the ferritic sulphate-sulfuric acid test and copper-copper sulphate-50% sulphuric acid test under a binocular microscope at 40x magnification. The bend test evaluations for the steel test specimens are presented.
SCOPE
1.1 These practices cover the following four tests:
1.1.1 Practice W—Oxalic acid etch test for detecting susceptibility to intergranular attack in stabilized ferritic stainless steels by classification of the etching structures (see Sections 3 through 10).
1.1.2 Practice X—Ferric sulfate-sulfuric acid test for detecting susceptibility to intergranular attack in ferritic stainless steels (Sections 11 to 16).
1.1.3 Practice Y—Copper-copper sulfate-50 % sulfuric acid test for detecting susceptibility to intergranular attack in ferritic stainless steels (Sections 17 to 22).
1.1.4 Practice Z—Copper-copper sulfate-16 % sulfuric acid test for detecting susceptibility to intergranular attack in ferritic stainless steels (Sections 23 to 29).
1.2 The following factors govern the application of these practices (1-6):
1.2.1 Practice W, oxalic acid test, is a rapid method of identifying, by simple, electrolytic etching, those specimens of certain ferritic alloys that are not susceptible to intergranular corrosion associated with chromium carbide precipitation. Practice W is used as a screening test to avoid the necessity, for acceptable specimens, of more extensive testing required by Practices X, Y, and Z. See Table 1 for a listing of alloys for which Practice W is appropriate.
1.2.2 Practices X, Y, and Z can be used to detect the susceptibility of certain ferritic alloys to intergranular attack associated with the precipitation of chromium carbides or nitrides.
1.2.3 Practices W, X, Y, and Z can also be used to evaluate the effect of heat treatment or of fusion welding on susceptibility to intergranular corrosion.
1.2.4 lists the identification ferritic stainless steels for which data on the application of at least one of the standard practices is available.
1.2.5 Some stabilized ferritic stainless steels may show high rates when tested by Practice X because of metallurgical factors not associated with chromium carbide or nitride precipitation. This possibility must be considered in selecting the test method. Combinations of alloys and test methods for which successful experience is available are shown in . Application of these standard tests to the other ferritic stainless steels will be by specific agreement between producer and user.
1.3 Depending on the test and alloy, evaluations may be accomplished by weight loss determination, microscopical examination, or bend test (Sections 30 and 31). The choices are listed in Table 1.
1.4 sibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. For specific safety precautionary statements, see 3.2.5, Section 7, 13.1, and 19.1.
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Designation:A763–93(Reapproved 2004)
Standard Practices for
Detecting Susceptibility to Intergranular Attack in Ferritic
Stainless Steels
This standard is issued under the fixed designation A 763; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 1.2.5 Some stabilized ferritic stainless steels may show high
rates when tested by Practice X because of metallurgical
1.1 These practices cover the following four tests:
factors not associated with chromium carbide or nitride pre-
1.1.1 Practice W—Oxalic acid etch test for detecting sus-
cipitation. This possibility must be considered in selecting the
ceptibility to intergranular attack in stabilized ferritic stainless
test method. Combinations of alloys and test methods for
steels by classification of the etching structures (see Sections 3
which successful experience is available are shown in Table 1.
through 10).
Application of these standard tests to the other ferritic stainless
1.1.2 PracticeX—Ferricsulfate-sulfuricacidtestfordetect-
steelswillbebyspecificagreementbetweenproduceranduser.
ing susceptibility to intergranular attack in ferritic stainless
1.3 Depending on the test and alloy, evaluations may be
steels (Sections 11 to 16).
accomplished by weight loss determination, microscopical
1.1.3 Practice Y—Copper-copper sulfate-50 % sulfuric acid
examination,orbendtest(Sections30and31).Thechoicesare
testfordetectingsusceptibilitytointergranularattackinferritic
listed in Table 1.
stainless steels (Sections 17 to 22).
1.4 This standard does not purport to address all of the
1.1.4 Practice Z—Copper-copper sulfate-16 % sulfuric acid
safety problems, if any, associated with its use. It is the
testfordetectingsusceptibilitytointergranularattackinferritic
responsibility of the user of this standard to establish appro-
stainless steels (Sections 23 to 29).
priate safety and health practices and determine the applica-
1.2 The following factors govern the application of these
bility of regulatory limitations prior to use. For specific safety
practices (1–6) :
precautionary statements, see 3.2.5, Section 7, 13.1, and 19.1.
1.2.1 Practice W, oxalic acid test, is a rapid method of
identifying, by simple, electrolytic etching, those specimens of
2. Referenced Documents
certain ferritic alloys that are not susceptible to intergranular
2.1 ASTM Standards:
corrosion associated with chromium carbide precipitation.
A 370 Test Methods and Definitions for MechanicalTesting
PracticeWisusedasascreeningtesttoavoidthenecessity,for
of Steel Products
acceptable specimens, of more extensive testing required by
Practices X, Y, and Z. See Table 1 for a listing of alloys for
3. Apparatus
which Practice W is appropriate.
3.1 Apparatus for Practice W, Oxalic Acid Etch Test:
1.2.2 Practices X, Y, and Z can be used to detect the
3.1.1 Source of DC—Battery, generator, or rectifier capable
susceptibility of certain ferritic alloys to intergranular attack
of supplying 15 V and 20 A.
associated with the precipitation of chromium carbides or
3.1.2 Ammeter, range 0 to 30 A.
nitrides.
3.1.3 Variable Resistance, for control of specimen current.
1.2.3 Practices W, X, Y, and Z can also be used to evaluate
3.1.4 Cathode—One-litre stainless steel beaker or suitable
the effect of heat treatment or of fusion welding on suscepti-
piece of stainless steel.
bility to intergranular corrosion.
3.1.5 Electric Clamp, to hold etched specimen.
1.2.4 Table 2 lists the identification ferritic stainless steels
3.1.6 Metallurgical Microscope, for examination of etched
for which data on the application of at least one of the standard
structures at 250 to 5003.
practices is available.
3.1.7 Electrodes—The specimen is made the anode and the
beaker or other piece of stainless steel the cathode.
3.1.8 Electrolyte—Oxalic acid (H C O ·2H O) reagent
2 2 4 2
These practices are under the jurisdiction of ASTM Committee A01 on Steel,
grade, 10 weight % solution.
StainlessSteelandRelatedAlloys,andarethedirectresponsibilityofSubcommittee
A01.14 on Methods of Corrosion Testing.
Current edition approved March 1, 2004. Published March 2004. Originally For referenced ASTM standards, visit the ASTM website, www.astm.org, or
e1
approved in 1979. Last previous edition approved in 1999 as A 763 – 93 (1999) . contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
The boldface numbers in parentheses refer to the list of references appended to Standards volume information, refer to the standard’s Document Summary page on
these practices. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
A763–93 (2004)
TABLE 1 Methods for Evaluating Ferritic Stainless Steels for Susceptibility to Intergranular Corrosion
Evaluation Criteria
Alloy Time of Test, h
Weight Loss Microscopical Bend Test
Examination
PRACTICE W—OXALIC ACID ETCH TEST
A
439 0.025 NA A NA
A
18Cr-2Mo 0.025 NA A NA
A
XM27 0.025 NA A NA
A
XM33 0.025 NA A NA
A
26-3-3 0.025 NA A NA
PRACTICE X—FERRIC SULFATE - SULFURIC ACID TEST
B,C
430 24 A ANA
C
446 72 A ANA
D C
XM27 120 A A NA
E C
29Cr-4Mo 120 NA A NA
C
29Cr-4Mo-2Ni 120 NA A NA
PRACTICE Y—COPPER-COPPER SULFATE - 50% SULFURIC ACID TEST
C
446 96 A ANA
D C
XM27 120 A A NA
D C
XM33 120 A A NA
D C
26–3–3 120 A A NA
D C
29-4C 120 A A NA
C
29Cr-4Mo 120 NA A NA
C
29Cr-4Mo-2Ni 120 NA A NA
PRACTICE Z—COPPER-COPPER SULFATE - 16% SULFURIC ACID TEST
430 24 NA NA no fissures
434 24 NA NA no fissures
436 24 NA NA no fissures
439 24 NA NA no fissures
18Cr-2Mo 24 NA NA no fissures
A
Polished surface examined at 250 to 5003 with a metallurgical microscope (see 3.1.6). All other microscopical examinations are of the corroded surface under 403
binocular examination (see Section 27).
B
A = Applicable.
C
Preferred criterion, these criteria are the most sensitive for the particular combination of alloy and test.
D
Weight loss measurements can be used to detect severely sensitized material, but they are not very sensitive for alloys noted with this superscript and may not detect
slight or moderate sensitization.
E
NA = Not applicable.
TABLE 2 Steels for Which Test Results are Available
3.2.3 Erlenmeyer Flask, 1-L with a 45/50 ground-glass
joint. The ground-glass opening is somewhat over 38 mm (1 ⁄2
UNS Designation Alloy Practice(s)
in.) wide.
A
S43000 430 X, Z
3.2.4 Glass Cradles (Note 2) can be supplied by a glass
A
S43400 434 Z
A
blowing shop. The size of the cradles should be such that they
S43600 436 Z
S43035 XM8 Z
can pass through the ground-glass joint of the Erlenmeyer
S44400 18Cr-2Mo W, Z
flask. They should have three or four holes in them to increase
A
S44600 446 X, Y
circulation of the test solution around the specimen.
S44626 XM33 W, Y
S44627 XM27 W, X, Y
S44660 26–3–3 Y NOTE 2—Other equivalent means of specimen support such as glass
S44700 29Cr-4Mo X, Y
hooks or stirrups may also be used.
S44735 29-4C Y
S44800 29Cr-4Mo-2NI X, Y
3.2.5 Boiling Chips, must be used to prevent bumping. It
A
has been reported that violent boiling resulting in acid spills
Types 430, 434, 436, and 446 are nonstabilized grades that are generally not
used in the as-welded or sensitized condition in other than mildly corrosive
can occur. It is important to ensure that the concentration of
environments. In the annealed condition, they are not subject to intergranular
acid does not become more concentrated and that an adequate
corrosion. For any studies of IGA on Types 430, 434, 436, or 446, the indicated test
methods are suggested.
number of boiling chips (which are resistant to attack by the
test solution) are present.
3.2 The apparatus common to Practices X,Y, and Z is listed 3.2.6 Silicone Grease, is recommended for the ground-glass
joint.
below. Supplementary requirements are noted as required.
3.2.1 The apparatus used is shown in Fig. 1.
3.2.7 Electrically Heated Hot Plate, or other device to
provide heat for continuous boiling of the solution.
NOTE 1—No substitution for this equipment may be used. The cold-
fingertypeofcondenserwithstandardErlenmeyerflasksmaynotbeused.
3.2.2 Allihn or Soxhlet Condenser, four-bulb (minimum)
with a 45/50 ground-glass joint. Overall length shall be about 4
Amphoteric alundum granules, Hengar Granules, from the Hengar Company,
⁄2 in.). Philadelphia, PA have been found satisfactory for this purpose.
330 mm (13 in.) with condensing section, 241 mm (9
A763–93 (2004)
4.4.1 Specimensfrommaterialthatisgoingtobeusedinthe
as-received condition without additional welding or heat treat-
ment may be tested in the as-received condition without any
sensitizing treatment.
4.4.2 Specimens from material that is going to be welded or
heat treated should be welded or heat treated in as nearly the
same manner as the material will experience in service.
4.4.3 The specific sensitizing or welding treatment, or both,
should be agreed upon between the supplier and the purchaser.
4.5 For Practice W, a cross section of the sample including
materialatbothsurfacesandacrosssectionofanyweldandits
heat affected zones should be prepared. If the sample is too
thick, multiple specimens should be used. Grind the cross
sectiononwetordry80or120-gritabrasivepaperfollowedby
successively finer papers until a number 400 or 3/0 finish is
obtained. Avoid excessive heat when dry-grinding.
4.6 For Practices X, Y, and Z, all surfaces of the specimen
including edges should be ground on wet or dry 80 or 120-grit
abrasive paper. Avoid excessive heat when dry-grinding. Do
not use sand- or grit-blasting. All traces of oxide scale formed
during heat treatment must be removed. To avoid scale
entrapment, stamp specimens for identification after heat
treatment and grinding.
4.7 Degrease and dry the sample using suitable nonchlori-
nated agents.
PRACTICE W—OXALIC ACID ETCH TEST FOR
DETECTING SUSCEPTIBILITY TO
FIG. 1 Test Apparatus
INTERGRANULAR ATTACK BY CLASSIFICATION
OF MICROSTRUCTURE FOR SCREENING OF
CERTAIN FERRITIC STAINLESS STEELS
4. Preparation of Test Specimens
5. Scope
4.1 The preparation of test specimens is common among
Practices X,Y, and Z.Additional requirements are noted where
5.1 Theoxalicacidetchtestisintendedandmaybeusedfor
necessary.
screening of certain ferritic stainless steels to precede or
precludetheneedforcorrosiontestingasdescribedinPractices
4.2 Aspecimen having a total surface area of 5 to 20 cm is
X, Y, or Z. Specimens with unacceptable microstructures
recommended for Practices X, Y, and Z.As-welded specimens
should be subjected to Practices X, Y, or Z to better determine
should be cut so that no more than 13 mm ⁄2 (in.) width of
their susceptibility to intergranular attack. See Table 1 for a
unaffectedbasemetalisincludedoneithersideoftheweldand
listing of alloys for which Practice W is appropriate.
heat-affected zone.
4.3 The intent is to test a specimen representing as nearly as
6. Etching Conditions
possible the surface of the material as used in service. Only
such surface finishing should be performed as is required to 6.1 The polished specimens should be etched at 1A/cm for
remove foreign material and obtain a standard, uniform finish 1.5 min. This may be accomplished with the apparatus pre-
scribed in 3.1 by adjusting the variable resistance until the
as specified. For very heavy sections, specimens should be
ammeter reading in amperes equals the immersed specimen
preparedtorepresenttheappropriatesurfacewhilemaintaining
area in square centimetres. Immersion of the specimen-holding
reasonable specimen size for convenience in testing. Ordi-
clamp in the etching solution should be avoided.
narily, removal of more material than necessary will have little
influence on the test results. However, in the special case of
7. Etching Precautions
surface carburization (sometimes encountered, for instance, in
tubing when carbonaceous lubricants are employed) it may be
7.1 Etching should be carried out under a ventilating hood.
possible by heavy grinding or machining to remove the
Gas evolved at the electrodes with entrained oxalic acid is
carburized layer completely. Such treatment of test specimens
poisonous and irritating. The temperature of the etching
is not permissible, except in tests undertaken to demonstrate
solution, which increases during etching, should be kept below
such surface effects.
50°C by using two beakers of acid, one of which may be
4.4 Sensitization of Test Specimens: cooled while the other is in use.
A763–93 (2004)
8. Rinsing Prior to Examination 10. Classification of Etched Structures
8.1 Following etching, the specimen should be rinsed in hot
10.1 Acceptable structures indicating resistance to chro-
water then acetone or alcohol to avoid oxalic acid crystalliza-
mium carbide-type intergranular attack:
tion on the etched surface during forced air-drying.
10.1.1 Step structure—Steps only between grains—no
ditches at grain boundaries (see Fig. 2).
9. Examination
10.1.2 Dual structure—Some ditches at grain boundaries in
9.1 Examine etched specimens on a metallurgical micro-
addition to steps, but no single grain completely surrounded by
scopeat250to5003asappropriateforclassificationofetched
ditches (see Fig. 3).
microstructure type as defined in Section 10.
FIG. 2 Acceptable Structures Practice W—Oxalic-Acid Etch Test Steps Between Grains No Ditching
A763–93 (2004)
FIG. 3 Acceptable Structure Practice W—Oxalic Acid Etch Test Dual Structure Some Ditches But No Single Grain Completely
Surrounded
10.2 Unacceptable structures requiring additional testing 12. Apparatus
(Practices X, Y, or Z):
12.1 The basic apparatus is described in Section 3. Also
10.2.1 Ditch structure—One or more grains completely
needed are:
surrounded by ditches (see Fig. 4).
12.1.1 For weight loss determination, an analytical balance
capable of weighing to at least the nearest 0.001 g.
PRACTICE X—FERRIC SULFATE-SULFURIC ACID
12.1.2 For microscopical examination, a microscope with
TEST FOR DETECTING SUSCEPTIBILITY TO
magnification to at least 403.
INTERGRANULAR ATTACK IN FERRITIC
STAINLESS STEELS
13. Ferric Sulfate-Sulfuric Acid Test Solution
11. Scope
13.1 Prepare 600 mL of test solution as follows.
(Warning—Protect the eyes and use rubber gloves and apron
11.1 This practice describes the procedure for conducting
the boiling ferric sulfate-sulfuric acid test which measures the for handling acid. Place the test flask under a hood.)
susceptibility o
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