ASTM A763 - 15 (2021)

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Designation: A763 −15 (Reapproved 2021)
Standard Practices for
Detecting Susceptibility to Intergranular Attack in Ferritic
Stainless Steels
1
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. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 These practices cover the following four tests:
1.1.1 Practice W—Oxalic acid etch test for detecting sus-
ceptibility to intergranular attack in stabilized ferritic stainless
steels by classiﬁcation of the etching structures (see Sections 3
–1
0).
1.1.2 Practice X—Ferric sulfate-sulfuric acid test for detect-
ing susceptibility to intergranular attack in ferritic stainless
steels (Sections 11–16).
1.1.3 Practice Y—Copper-copper sulfate-50 % sulfuric acid
test for detecting susceptibility to intergranular attack in ferritic
stainless steels (Sections 17–22).
1.1.4 Practice Z—Copper-copper sulfate-16 % sulfuric acid
test for detecting susceptibility to intergranular attack in ferritic
stainless steels (Sections 23–29).
1.2 The following factors govern the application of these
practices (1-6):
2
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 suscepti-
bility 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 pre-
cipitation. 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 concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
For speciﬁc safety precautionary statements, see 3.2.5, Section
7,13.1, and 19.1.
1.5 This international standard was developed in accor-
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
3
A370 Test Methods and Deﬁnitions for Mechanical Testing
of Steel Products
1
These practices are under the jurisdiction of ASTM Committee A01 on Steel,
Stainless Steel and Related Alloys and are the direct responsibility of Subcommittee
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:
10.1520/A0763-15R21.
2
The boldface numbers in parentheses refer to the list of references appended to
these practices.
3
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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.
1

3. Apparatus

3.1 Apparatus for Practice W, Oxalic Acid Etch Test:

3.1.1 Source of DC—Battery, generator, or rectiﬁer capable

of supplying 15 V and 20 A.

3.1.2 Ammeter, range 0 to 30 A.

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.

3.1.6 Metallurgical Microscope, for examination of etched

structures at 250 to 500×.

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

·2H

O) reagent

grade, 10 weight % solution.

3.2 Aparatus Common to Practices X, Y, and

Z—Suplementary requirements are noted as required.

3.2.1 The apparatus used is shown in Fig. 1.

NOTE 1—No substitution for this equipment may be used. The

cold-ﬁnger type of condenser with standard Erlenmeyer ﬂasks may not be

used.

3.2.2 Allihn or Soxhlet Condenser, four-bulb (minimum)

with a 45/50 ground-glass joint. Overall length shall be about

330 mm (13 in.), with condensing section 241 mm (9

⁄

in.).

3.2.3 Erlenmeyer Flask, 1 L with a 45/50 ground-glass joint.

The ground-glass opening is somewhat over 38 mm (1

⁄

in.)

wide.

3.2.4 Glass Cradles (Note 2), can be supplied by a glass

blowing shop. The size of the cradles should be such that they

can pass through the ground-glass joint of the Erlenmeyer

ﬂask. They should have three or four holes in them to increase

circulation of the test solution around the specimen.

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

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

439 0.025 NA A

18Cr-2Mo 0.025 NA A

XM27 0.025 NA A

XM33 0.025 NA A

26-3-3 0.025 NA A

PRACTICE X—FERRIC SULFATE - SULFURIC ACID TEST

430 24 A

B,C

ANA

446 72 A

ANA

XM27 120 A

29Cr-4Mo 120 NA

29Cr-4Mo-2Ni 120 NA A

PRACTICE Y—COPPER-COPPER SULFATE - 50% SULFURIC ACID TEST

446 96 A

ANA

XM27 120 A

XM33 120 A

26–3–3 120 A

29-4C 120 A

29Cr-4Mo 120 NA A

29Cr-4Mo-2Ni 120 NA A

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

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).

A = Applicable.

Preferred criterion, these criteria are the most sensitive for the particular combination of alloy and test.

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.

NA = Not applicable.

TABLE 2 Steels for Which Test Results are Available

UNS Designation Alloy Practice(s)

S43000 430

X, Z

S43400 434

S43600 436

S43035 439 W, Z

S44400 18Cr-2Mo W, Z

S44600 446

X, Y

S44626 XM33 W, Y

S44627 XM27 W, X, Y

S44660 26–3–3 W, Y

S44700 29Cr-4Mo X, Y

S44735 29-4C Y

S44800 29Cr-4Mo-2NI X, Y

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

environments. In the annealed condition, they are not subject to intergranular

corrosion. For any studies of IGA on Types 430, 434, 436, or 446, the indicated test

methods are suggested.

A763 − 15 (2021)

can occur. It is important to ensure that the concentration of

acid does not become more concentrated and that an adequate

number of boiling chips (which are resistant to attack by the

test solution) are present.

NOTE 3—Amphoteric alundum granules, Hengar Granules, from the

Hengar Company, Philadelphia, PA have been found satisfactory for this

purpose.

3.2.6 Silicone Grease, is recommended for the ground-glass

joint.

3.2.7 Electrically Heated Hot Plate, or other device to

provide heat for continuous boiling of the solution.

4. Preparation of Test Specimens

4.1 The preparation of test specimens is common among

Practices X, Y, and Z. Additional requirements are noted where

necessary.

4.2 A specimen having a total surface area of 5 to 20 cm

recommended for Practices X, Y, and Z. As-welded specimens

should be cut so that no more than 13 mm (

⁄

in.) width of

unaffected base metal is included on either side of the weld and

heat-affected zone.

4.3 The intent is to test a specimen representing as nearly as

possible the surface of the material as used in service. Only

such surface ﬁnishing should be performed as is required to

remove foreign material and obtain a standard, uniform ﬁnish

as speciﬁed. For very heavy sections, specimens should be

prepared to represent the appropriate surface while maintaining

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 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

INTERGRANULAR ATTACK BY CLASSIFICATION

OF MICROSTRUCTURE FOR SCREENING OF

CERTAIN FERRITIC STAINLESS STEELS

5. Scope

5.1 The oxalic acid etch test is intended and may be used for

screening of certain ferritic stainless steels to precede or

preclude the need for corrosion testing as described in Practices

X, Y, or Z. Specimens with unacceptable microstructures

should be subjected to Practices X, Y, or Z to better determine

their susceptibility to intergranular attack. See Table 1 for a

listing of alloys for which Practice W is appropriate.

6. Etching Conditions

6.1 The polished specimens should be etched at 1 A/cm

for

1.5 min. This may be accomplished with the apparatus pre-

scribed in 3.1 by adjusting the variable resistance until the

ammeter reading in amperes equals the immersed specimen

FIG. 1 Test Apparatus

A763 − 15 (2021)

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摘要：

ASTM A763 - 15 (2021) 是美国材料与试验协会发布的关于检测不锈钢晶间腐蚀敏感性的标准测试方法。该标准涵盖了对铁素体不锈钢及部分奥氏体-铁素体双相不锈钢的特定腐蚀环境下的试验程序，包括草酸浸蚀试验、硫酸-硫酸铁试验、硝酸-氢氟酸试验以及硫酸-硫酸铜试验。通过本标准的测试，可有效评估材料在焊接或热加工后是否易于发生晶间腐蚀失效，从而为不锈钢在化工、能源、食品加工等领域的选材与质量控制提供可靠依据。2021年版本延续了2015年的技术要求，确保与现行工业实践及材料性能评估需求保持一

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