ASTM A763-93(1999)e1

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
e1
Designation: A 763 – 93 (Reapproved 1999)
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.
e NOTE—Keywords were added editorially in March 1999.
1. Scope 1.2.4 Table 2 lists the identification ferritic stainless steels
for which data on the application of at least one of the standard
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 Some stabilized ferritic stainless steels may show high
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 Practice X—Ferric sulfate-sulfuric acid test for detect-
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).
Application of these standard tests to the other ferritic stainless
1.1.3 Practice Y—Copper-copper sulfate-50 % sulfuric acid
steels will be by specific agreement between producer and user.
test for detecting susceptibility to intergranular attack in ferritic
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, or bend test (Sections 30 and 31). The choices are
test for detecting susceptibility to intergranular attack in ferritic
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-
1.2.1 Practice W, oxalic acid test, is a rapid method of
priate safety and health practices and determine the applica-
identifying, by simple, electrolytic etching, those specimens of
bility of regulatory limitations prior to use. For specific safety
certain ferritic alloys that are not susceptible to intergranular
precautionary statements, see 3.2.5, Section 7, 13.1, and 19.1.
corrosion associated with chromium carbide precipitation.
Practice W is used as a screening test to avoid the necessity, for
2. Referenced Documents
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
A 370 Test 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.
These practices are under the jurisdiction of ASTM Committee A-1 on Steel,
Stainless Steel, and Related Alloys,and are the direct responsibility of Subcommittee
3.1.5 Electric Clamp, to hold etched specimen.
A01.14 on Methods of Corrosion Testing.
Current edition approved July 15, 1993. Published September 1993. Originally
published as A 763 – 79. Last previous edition A 763 – 90.
The boldface numbers in parentheses refer to the list of references appended to
these practices. Annual Book of ASTM Standards, Vol 01.03.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
e1
A 763 – 93 (1999)
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 finger type of condenser with standard Erlenmeyer flasks may not be used.
3.2.2 Allihn or Soxhlet Condenser, four-bulb (minimum)
UNS Designation Alloy Practice(s)
with a 45/50 ground-glass joint. Overall length shall be about
A
S43000 430 X, Z
A 330 mm (13 in.) with condensing section, 241 mm (9 ⁄2 in.).
S43400 434 Z
A
S43600 436 Z 3.2.3 Erlenmeyer Flask, 1-L with a 45/50 ground-glass
S43035 XM8 Z
joint. The ground-glass opening is somewhat over 38 mm (1 ⁄2
S44400 18Cr-2Mo W, Z
A in.) wide.
S44600 446 X, Y
S44626 XM33 W, Y 3.2.4 Glass Cradles (Note 2) can be supplied by a glass
S44627 XM27 W, X, Y
blowing shop. The size of the cradles should be such that they
S44660 26–3–3 Y
can pass through the ground-glass joint of the Erlenmeyer
S44700 29Cr-4Mo X, Y
S44735 29-4C Y
flask. They should have three or four holes in them to increase
S44800 29Cr-4Mo-2NI X, Y
circulation of the test solution around the specimen.
A
Types 430, 434, 436, and 446 are nonstabilized grades that are generally not
NOTE 2—Other equivalent means of specimen support such as glass
used in the as-welded or sensitized condition in other than mildly corrosive
environments. In the annealed condition, they are not subject to intergranular hooks or stirrups may also be used.
corrosion. For any studies of IGA on Types 430, 434, 436, or 446, the indicated test
3.2.5 Boiling Chips, must be used to prevent bumping. It
methods are suggested.
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 5003.
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.
test solution) are present.
3.1.8 Electrolyte—Oxalic acid (H C O ·2H O) reagent 3.2.6 Silicone Grease, is recommended for the ground-glass
2 2 4 2
grade, 10 weight % solution.
joint.
3.2 The apparatus common to Practices X, Y, and Z is listed
below. Supplementary requirements are noted as required.
3.2.1 The apparatus used is shown in Fig. 1.
Amphoteric alundum granules, Hengar Granules, from the Hengar Company,
NOTE 1—No substitution for this equipment may be used. The cold- Philadelphia, PA have been found satisfactory for this purpose.
e1
A 763 – 93 (1999)
4.4 Sensitization of Test Specimens:
4.4.1 Specimens from material that is going to be used in the
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
material at both surfaces and a cross section of any weld and its
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
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
3.2.7 Electrically Heated Hot Plate, or other device to
provide heat for continuous boiling of the solution.
5. Scope
4. Preparation of Test Specimens
5.1 The oxalic acid etch test is intended and may be used for
4.1 The preparation of test specimens is common among
screening of certain ferritic stainless steels to precede or
Practices X, Y, and Z. Additional requirements are noted where
preclude the need for corrosion testing as described in Practices
necessary.
X, Y, or Z. Specimens with unacceptable microstructures
4.2 A specimen 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.
unaffected base metal is included on either side of the weld and
heat-affected zone.
6. Etching Conditions
4.3 The intent is to test a specimen representing as nearly as
6.1 The polished specimens should be etched at 1 A/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
area in square centimetres. Immersion of the specimen-holding
prepared to represent the appropriate surface while maintaining
clamp in the etching solution should be avoided.
reasonable specimen size for convenience in testing. Ordi-
narily, removal of more material than necessary will have little
7. Etching Precautions
influence on the test results. However, in the special case of
surface carburization (sometimes encountered, for instance, in 7.1 Etching should be carried out under a ventilating hood.
tubing when carbonaceous lubricants are employed) it may be Gas evolved at the electrodes with entrained oxalic acid is
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, which increases during etching, should be kept below
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.
e1
A 763 – 93 (1999)
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
scope at 250 to 5003 as appropriate for classification of etched
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
e1
A 763 – 93 (1999)
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. Caution—
Protect the eyes and use rubber gloves and apron for handling
11.1 This practice describes the procedure for conducting
the boiling ferric sulfate-sulfuric acid test which measures the acid. Place the test flask u
...