ASTM A763-15(2021)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: A763 − 15 (Reapproved 2021)
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-
–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 (Sections11–16).
Applicationofthesestandardteststotheotherferriticstainless
1.1.3 Practice Y—Copper-copper sulfate-50% sulfuric acid
steelswillbebyspecificagreementbetweenproduceranduser.
testfordetectingsusceptibilitytointergranularattackinferritic
stainless steels (Sections17–22).
1.3 Depending on the test and alloy, evaluations may be
1.1.4 Practice Z—Copper-copper sulfate-16% sulfuric acid
accomplished by weight loss determination, microscopical
testfordetectingsusceptibilitytointergranularattackinferritic
examination,orbendtest(Sections30and31).Thechoicesare
stainless steels (Sections23–29).
listed in Table 1.
1.2 The following factors govern the application of these
1.4 This standard does not purport to address all of the
practices (1-6):
safety concerns, if any, associated with its use. It is the
1.2.1 Practice W, oxalic acid test, is a rapid method of
responsibility of the user of this standard to establish appro-
identifying, by simple electrolytic etching, those specimens of
priate safety, health, and environmental practices and deter-
certain ferritic alloys that are not susceptible to intergranular
mine the applicability of regulatory limitations prior to use.
corrosion associated with chromium carbide precipitation.
For specific safety precautionary statements, see 3.2.5, Section
PracticeWisusedasascreeningtesttoavoidthenecessity,for
7, 13.1, and 19.1.
acceptable specimens, of more extensive testing required by
1.5 This international standard was developed in accor-
Practices X, Y, and Z. See Table 1 for a listing of alloys for
dance with internationally recognized principles on standard-
which Practice W is appropriate.
ization established in the Decision on Principles for the
1.2.2 Practices X, Y, and Z can be used to detect the
Development of International Standards, Guides and Recom-
susceptibility of certain ferritic alloys to intergranular attack
mendations issued by the World Trade Organization Technical
associated with the precipitation of chromium carbides or
Barriers to Trade (TBT) Committee.
nitrides.
1.2.3 Practices W, X, Y, and Z can also be used to evaluate
2. Referenced Documents
the effect of heat treatment or of fusion welding on suscepti-
bility to intergranular corrosion. 2.1 ASTM Standards:
A370Test Methods and Definitions for Mechanical Testing
1 of Steel Products
These practices are under the jurisdiction of ASTM Committee A01 on Steel,
StainlessSteelandRelatedAlloysandarethedirectresponsibilityofSubcommittee
A01.14 on Methods of Corrosion Testing.
Current edition approved Sept. 1, 2021. Published September 2021. Originally
approved in 1979. Last previous edition approved in 2015 as A763–15. DOI: For referenced ASTM standards, visit the ASTM website, www.astm.org, or
10.1520/A0763-15R21. 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 − 15 (2021)
TABLE 1 Methods for Evaluating Ferritic Stainless Steels for Susceptibility to Intergranular Corrosion
Evaluation Criteria
Alloy Time of Test, h
Weight Loss Microscopical Examination Bend Test
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
3.1.6 Metallurgical Microscope, for examination of etched
UNS Designation Alloy Practice(s) structures at 250 to 500×.
A
S43000 430 X, Z
3.1.7 Electrodes—The specimen is made the anode and the
A
S43400 434 Z
A beaker or other piece of stainless steel the cathode.
S43600 436 Z
S43035 439 W, Z 3.1.8 Electrolyte—Oxalic acid (H C O ·2H O) reagent
2 2 4 2
S44400 18Cr-2Mo W, Z
grade, 10 weight% solution.
A
S44600 446 X, Y
S44626 XM33 W, Y
3.2 Aparatus Common to Practices X, Y, and
S44627 XM27 W, X, Y
Z—Suplementary requirements are noted as required.
S44660 26–3–3 W, Y
3.2.1 The apparatus used is shown in Fig. 1.
S44700 29Cr-4Mo X, Y
S44735 29-4C Y
NOTE 1—No substitution for this equipment may be used. The
S44800 29Cr-4Mo-2NI X, Y
cold-finger type of condenser with standard Erlenmeyer flasks may not be
A
Types 430, 434, 436, and 446 are nonstabilized grades that are generally not
used.
used in the as-welded or sensitized condition in other than mildly corrosive
environments. In the annealed condition, they are not subject to intergranular
3.2.2 Allihn or Soxhlet Condenser, four-bulb (minimum)
corrosion. For any studies of IGA on Types 430, 434, 436, or 446, the indicated test
with a 45/50 ground-glass joint. Overall length shall be about
methods are suggested.
330 mm (13 in.), with condensing section 241 mm (9 ⁄2 in.).
3.2.3 ErlenmeyerFlask,1Lwitha45/50ground-glassjoint.
The ground-glass opening is somewhat over 38 mm (1 ⁄2in.)
wide.
3.2.4 Glass Cradles (Note 2), can be supplied by a glass
3. Apparatus
blowing shop. The size of the cradles should be such that they
3.1 Apparatus for Practice W, Oxalic Acid Etch Test:
can pass through the ground-glass joint of the Erlenmeyer
3.1.1 Source of DC—Battery, generator, or rectifier capable
flask.They should have three or four holes in them to increase
of supplying 15 V and 20 A.
circulation of the test solution around the specimen.
3.1.2 Ammeter, range 0 to 30 A.
NOTE 2—Other equivalent means of specimen support such as glass
3.1.3 Variable Resistance, for control of specimen current.
hooks or stirrups may also be used.
3.1.4 Cathode—One-litre stainless steel beaker or suitable
piece of stainless steel. 3.2.5 Boiling Chips, must be used to prevent bumping. It
3.1.5 Electric Clamp, to hold etched specimen. has been reported that violent boiling resulting in acid spills
A763 − 15 (2021)
preparedtorepresenttheappropriatesurfacewhilemaintaining
reasonable specimen size for convenience in testing.
Ordinarily, removal of more material than necessary will have
little influence on the test results. However, in the special case
of surface carburization (sometimes encountered, for instance,
in tubing when carbonaceous lubricants are employed) it may
be possible by heavy grinding or machining to remove the
carburized layer completely. Such treatment of test specimens
is not permissible, except in tests undertaken to demonstrate
such surface effects.
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
section on wet or dry 80- or 120-grit abrasive paper followed
by 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
FIG. 1 Test Apparatus
includingedgesshouldbegroundonwetordry80-or120-grit
abrasive paper. Avoid excessive heat when dry-grinding. Do
not use sand- or grit-blasting.All traces of oxide scale formed
can occur. It is important to ensure that the concentration of
during heat treatment must be removed. To avoid scale
acid does not become more concentrated and that an adequate
entrapment, stamp specimens for identification after heat
number of boiling chips (which are resistant to attack by the
treatment and grinding.
test solution) are present.
4.7 Degrease and dry the sample using suitable nonchlori-
NOTE 3—Amphoteric alundum granules, Hengar Granules, from the
nated agents.
Hengar Company, Philadelphia, PA have been found satisfactory for this
purpose.
PRACTICE W—OXALIC ACID ETCH TEST FOR
3.2.6 Silicone Grease,isrecommendedfortheground-glass
DETECTING SUSCEPTIBILITY TO
joint.
INTERGRANULAR ATTACK BY CLASSIFICATION
3.2.7 Electrically Heated Hot Plate, or other device to
OF MICROSTRUCTURE FOR SCREENING OF
provide heat for continuous boiling of the solution.
CERTAIN FERRITIC STAINLESS STEELS
4. Preparation of Test Specimens
5. Scope
4.1 The preparation of test specimens is common among
5.1 Theoxalicacidetchtestisintendedandmaybeusedfor
PracticesX,Y,andZ.Additionalrequirementsarenotedwhere
screening of certain ferritic stainless steels to precede or
necessary.
precludetheneedforcorrosiontestingasdescribedinPractices
X, Y, or Z. Specimens with unacceptable microstructures
4.2 Aspecimen having a total surface area of 5 to 20 cm is
recommended for Practices X,Y, and Z.As-welded specimens should be subjected to Practices X,Y, or Z to better determine
their susceptibility to intergranular attack. See Table 1 for a
should be cut so that no more than 13 mm ( ⁄2in.) width of
unaffectedbasemetalisincludedoneithersideoftheweldand listing of alloys for which Practice W is appropriate.
heat-affected zone.
6. Etching Conditions
4.3 Theintentistotestaspecimenrepresentingasnearlyas
possible the surface of the material as used in service. Only 6.1 Thepolishedspecimensshouldbeetchedat1A/cm for
such surface finishing should be performed as is required to 1.5 min. This may be accomplished with the apparatus pre-
remove foreign material and obtain a standard, uniform finish 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
A763 − 15 (2021)
areainsquarecentimetres.Immersionofthespecimen-holding 11.3 This procedure may be used on ferritic stainless steels
clamp in the etching solution should be avoided. after an appropriate sensitizing heat treatment or welding
procedure as agreed upon between the supplier and the
7. Etching Precautions
purchaser.
7.1 Etching should be carried out under a ventilating hood.
12. Apparatus
Gas evolved at the electrodes with entrained oxalic acid is
12.1 The basic apparatus is described in Section 3. Also
poisonous and irritating. The temperature of the etching
needed are:
solution,whichincreasesduringetching,shouldbekeptbelow
12.1.1 For weight loss determination, an analytical balance
50 °C by using two beakers of acid, one of which may be
capable of weighing to at least the nearest 0.001 g.
cooled while the other is in use.
12.1.2 For microscopical examination, a microscope with
magnification to at least 40×.
8. Rinsing Prior to Examination
13. Ferric Sulfate-Sulfuric Acid Test Solution
8.1 Following etching, the specimen should be rinsed in hot
water then acetone or alcohol to avoid oxalic acid crystalliza-
13.1 Prepare 600 mL of test solution as follows.
tion on the etched surface during forced air-drying.
(Warning—Protect the eyes and use rubber gloves and apron
for handling acid. Place the test flask under a hood.)
9. Examination
13.1.1 First, measure 400.0 mL of distilled water in a 500
9.1 Examine etched specimens on a metallurgical micro-
mL graduate and pour into the Erlenmeyer flask.
scope at 250 to 500× as appropriate for classification of etched 13.1.2 Then measure 236.0 mL of reagent grade sulfuric
microstructure type as defined in Section 10.
acid of a concentration that must be in the range from 95.0 to
98.0 weight% in at 250 mL graduate. Add the acid slowly to
10. Classification of Etched Structures the water in the Erlenmeyer flask to avoid boiling by the heat
evolved.
10.1 Acceptable structures indicating resistance to chro-
mium carbide-type intergranular attack:
NOTE 4—Loss of vapor results in co
...