ASTM A763-93(2009)
(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 Table 2 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 Table 1. 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 This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility 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.
TABLE 1 Methods for Evaluating Ferritic Stainless Steels for Susceptibility to Intergranular Corrosion Alloy
Time of Test, h
Evaluation Criteria
Weight Loss
Microscopical
Examination
Bend Test
PRACTICE W—OXALIC ACID ETCH TEST
4390.025NAAANA 18Cr-2Mo0.025NAAANA XM270.025NAAANA XM330.025NAAANA 26...
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: A763 − 93(Reapproved 2009)
Standard Practices for
Detecting Susceptibility to Intergranular Attack in Ferritic
Stainless Steels
This standard is issued under the fixed designation A763; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 1.2.4 Table 2 lists the identification ferritic stainless steels
forwhichdataontheapplicationofatleastoneofthestandard
1.1 These practices cover the following four tests:
practices is available.
1.1.1 Practice W—Oxalic acid etch test for detecting sus-
1.2.5 Somestabilizedferriticstainlesssteelsmayshowhigh
ceptibility to intergranular attack in stabilized ferritic stainless
rates when tested by Practice X because of metallurgical
steels by classification of the etching structures (see Sections 3
factors not associated with chromium carbide or nitride pre-
through 10).
cipitation. This possibility must be considered in selecting the
1.1.2 PracticeX—Ferricsulfate-sulfuricacidtestfordetect-
test method. Combinations of alloys and test methods for
ing susceptibility to intergranular attack in ferritic stainless
which successful experience is available are shown in Table 1.
steels (Sections 11 to 16).
Applicationofthesestandardteststotheotherferriticstainless
1.1.3 Practice Y—Copper-copper sulfate-50% sulfuric acid
steelswillbebyspecificagreementbetweenproduceranduser.
testfordetectingsusceptibilitytointergranularattackinferritic
1.3 Depending on the test and alloy, evaluations may be
stainless steels (Sections 17 to 22).
accomplished by weight loss determination, microscopical
1.1.4 Practice Z—Copper-copper sulfate-16% sulfuric acid
examination,orbendtest(Sections30and31).Thechoicesare
testfordetectingsusceptibilitytointergranularattackinferritic
listed in Table 1.
stainless steels (Sections 23 to 29).
1.4 This standard does not purport to address all of the
1.2 The following factors govern the application of these safety problems, if any, associated with its use. It is the
practices (1-6) : responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
1.2.1 Practice W, oxalic acid test, is a rapid method of
bility of regulatory limitations prior to use. For specific safety
identifying, by simple, electrolytic etching, those specimens of
precautionary statements, see 3.2.5, Section 7, 13.1, and 19.1.
certain ferritic alloys that are not susceptible to intergranular
corrosion associated with chromium carbide precipitation.
2. Referenced Documents
PracticeWisusedasascreeningtesttoavoidthenecessity,for
acceptable specimens, of more extensive testing required by
2.1 ASTM Standards:
Practices X, Y, and Z. See Table 1 for a listing of alloys for
A370Test Methods and Definitions for Mechanical Testing
which Practice W is appropriate.
of Steel Products
1.2.2 Practices X, Y, and Z can be used to detect the
susceptibility of certain ferritic alloys to intergranular attack
3. Apparatus
associated with the precipitation of chromium carbides or
3.1 Apparatus for Practice W, Oxalic Acid Etch Test:
nitrides.
3.1.1 Source of DC—Battery, generator, or rectifier capable
1.2.3 Practices W, X, Y, and Z can also be used to evaluate
of supplying 15 V and 20 A.
the effect of heat treatment or of fusion welding on suscepti-
3.1.2 Ammeter, range 0 to 30 A.
bility to intergranular corrosion.
3.1.3 Variable Resistance, for control of specimen current.
3.1.4 Cathode—One-litre stainless steel beaker or suitable
piece of stainless steel.
3.1.5 Electric Clamp, to hold etched specimen.
These practices are under the jurisdiction of ASTM Committee A01 on Steel,
StainlessSteelandRelatedAlloysandarethedirectresponsibilityofSubcommittee
A01.14 on Methods of Corrosion Testing.
Current edition approved April 1, 2009. Published April 2009. Originally
approved in 1979. Last previous edition approved in 2004 as A763–93(2004). For referenced ASTM standards, visit the ASTM website, www.astm.org, or
DOI: 10.1520/A0763-93R09. 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 (2009)
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 500× with a metallurgical microscope (see 3.1.6). All other microscopical examinations are of the corroded surface under 40×
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
NOTE 1—No substitution for this equipment may be used. The
cold-finger type of condenser with standard Erlenmeyer flasks may not be
UNS Designation Alloy Practice(s)
A
used.
S43000 430 X, Z
A
S43400 434 Z
3.2.2 Allihn or Soxhlet Condenser, four-bulb (minimum)
A
S43600 436 Z
with a 45/50 ground-glass joint. Overall length shall be about
S43035 XM8 Z
S44400 18Cr-2Mo W, Z
330 mm (13 in.) with condensing section, 241 mm (9 ⁄2 in.).
A
S44600 446 X, Y
3.2.3 Erlenmeyer Flask, 1-L with a 45/50 ground-glass
S44626 XM33 W, Y
joint.The ground-glass opening is somewhat over 38 mm (1 ⁄2
S44627 XM27 W, X, Y
S44660 26–3–3 Y
in.) wide.
S44700 29Cr-4Mo X, Y
3.2.4 Glass Cradles (Note 2) can be supplied by a glass
S44735 29-4C Y
blowing shop. The size of the cradles should be such that they
S44800 29Cr-4Mo-2NI X, Y
A can pass through the ground-glass joint of the Erlenmeyer
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 flask.They should have three or four holes in them to increase
environments. In the annealed condition, they are not subject to intergranular
circulation of the test solution around the specimen.
corrosion. For any studies of IGA on Types 430, 434, 436, or 446, the indicated test
methods are suggested.
NOTE 2—Other equivalent means of specimen support such as glass
hooks or stirrups may also be used.
3.2.5 Boiling Chips, must be used to prevent bumping. It
has been reported that violent boiling resulting in acid spills
3.1.6 Metallurgical Microscope, for examination of etched
can occur. It is important to ensure that the concentration of
structures at 250 to 500×.
acid does not become more concentrated and that an adequate
3.1.7 Electrodes—The specimen is made the anode and the
number of boiling chips (which are resistant to attack by the
beaker or other piece of stainless steel the cathode. 4
test solution) are present.
3.1.8 Electrolyte—Oxalic acid (H C O ·2H O) reagent
2 2 4 2
3.2.6 SiliconeGrease,isrecommendedfortheground-glass
grade, 10 weight% solution.
joint.
3.2 TheapparatuscommontoPracticesX,Y,andZislisted
below. Supplementary requirements are noted as required.
Amphoteric alundum granules, Hengar Granules, from the Hengar Company,
3.2.1 The apparatus used is shown in Fig. 1. Philadelphia, PA have been found satisfactory for this purpose.
A763 − 93 (2009)
4.4 Sensitization of Test Specimens:
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 Specimensfrommaterialthatisgoingtobeweldedor
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
3.2.7 Electrically Heated Hot Plate, or other device to
CERTAIN FERRITIC STAINLESS STEELS
provide heat for continuous boiling of the solution.
4. Preparation of Test Specimens 5. Scope
5.1 Theoxalicacidetchtestisintendedandmaybeusedfor
4.1 The preparation of test specimens is common among
PracticesX,Y,andZ.Additionalrequirementsarenotedwhere screening of certain ferritic stainless steels to precede or
precludetheneedforcorrosiontestingasdescribedinPractices
necessary.
2 X, Y, or Z. Specimens with unacceptable microstructures
4.2 Aspecimen having a total surface area of 5 to 20 cm is
should be subjected to Practices X,Y, or Z to better determine
recommended for Practices X,Y, and Z.As-welded specimens
their susceptibility to intergranular attack. See Table 1 for a
should be cut so that no more than 13 mm ⁄2 (in.) width of
listing of alloys for which Practice W is appropriate.
unaffectedbasemetalisincludedoneithersideoftheweldand
heat-affected zone.
6. Etching Conditions
4.3 Theintentistotestaspecimenrepresentingasnearlyas
6.1 Thepolishedspecimensshouldbeetchedat1A/cm for
possible the surface of the material as used in service. Only
1.5 min. This may be accomplished with the apparatus pre-
such surface finishing should be performed as is required to
scribed in 3.1 by adjusting the variable resistance until the
remove foreign material and obtain a standard, uniform finish
ammeter reading in amperes equals the immersed specimen
as specified. For very heavy sections, specimens should be
areainsquarecentimetres.Immersionofthespecimen-holding
preparedtorepresenttheappropriatesurfacewhilemaintaining
clamp in the etching solution should be avoided.
reasonable specimen size for convenience in testing.
Ordinarily, removal of more material than necessary will have
7. Etching Precautions
little influence on the test results. However, in the special case
of surface carburization (sometimes encountered, for instance, 7.1 Etching should be carried out under a ventilating hood.
in tubing when carbonaceous lubricants are employed) it may Gas evolved at the electrodes with entrained oxalic acid is
be possible by heavy grinding or machining to remove the poisonous and irritating. The temperature of the etching
carburized layer completely. Such treatment of test specimens solution,whichincreasesduringetching,shouldbekeptbelow
is not permissible, except in tests undertaken to demonstrate 50°C by using two beakers of acid, one of which may be
such surface effects. cooled while the other is in use.
A763 − 93 (2009)
8. Rinsing Prior to Examination 12.1.1 For weight loss determination, an analytical balance
capable of weighing to at least the nearest 0.001 g.
8.1 Following etching, the specimen should be rinsed in hot
12.1.2 For microscopical examination, a microscope with
water then acetone or alcohol to avoid oxalic acid crystalliza-
magnification to at least 40×.
tion on the etched surface during forced air-drying.
9. Examination
13. Ferric Sulfate-Sulfuric Acid Test Solution
9.1 Examine etched specimens on a metallurgical micro-
13.1 Prepare 600 mL of test solution as follows.
scope at 250 to 500× as appropriate for classification of etched
(Warning— Protect the eyes and use rubber gloves and apron
microstructure type as defined in Section 10.
for handling acid. Place the test flask under a hood.)
13.1.1 First, measure 400.0 mL of distilled water in a
10. Classification of Etched Structures
500-mL graduate and pour into the Erlenmeyer flask.
10.1 Acceptable structures indicating resistance to chro-
13.1.2 Then measure 236.0 mL of reagent grade sulfuric
mium carbide-type intergranular attack:
acid of a concentration that must be in the range from 95.0 to
10.1.1 Step structure—Steps only between grains—no
98.0 weight% in at 250-mL graduate. Add the acid slowly to
ditches at grain boundaries (see Fig. 2).
the water in the Erlenmeyer flask to avoid boiling by the heat
10.1.2 Dual structure—Some ditches at grain boundaries in
evolved.
additiontosteps,butnosinglegraincompletelysurroundedby
NOTE 3—Loss of vapor results in concentration of the acid.
ditches (see Fig. 3).
13.1.3 Weigh 25 g of reagent grade ferric sulfate (contains
10.2 Unacceptable structures requiring additional testing
about 75% Fe (SO ) ) and add to the sulfuric acid solution.A
2 4 3
(Practices X, Y, or Z):
trip balance may be used.
10.2.1 Ditch structure—One or more grains completely
13.1.4 Drop boiling chips into the flask.
surrounded by ditches (see Fig. 4).
13.1.5 Lubricatetheground-glassjointwithsiliconegrease.
13.1.6 Cover the flask with the condenser and circulate
PRACTICE X—
...
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