ASTM A763 - 93(2009)

    Standard Practices for Detecting Susceptibility to Intergranular Attack in Ferritic Stainless Steels

    Active Standard ASTM A763 | Developed by Subcommittee: A01.14

    Book of Standards Volume: 01.03

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    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.

    This abstract is a brief summary of the referenced standard. It is informational only and not an official part of the standard; the full text of the standard itself must be referred to for its use and application. ASTM does not give any warranty express or implied or make any representation that the contents of this abstract are accurate, complete or up to date.

    1. Scope

    1.1 These practices cover the following four tests:

    1.1.1 Practice WOxalic 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 XFerric sulfate-sulfuric acid test for detecting susceptibility to intergranular attack in ferritic stainless steels (Sections 11 to 16).

    1.1.3 Practice YCopper-copper sulfate-50 % sulfuric acid test for detecting susceptibility to intergranular attack in ferritic stainless steels (Sections 17 to 22).

    1.1.4 Practice ZCopper-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

    Time of Test, h
    Evaluation Criteria
    Weight Loss
    Bend Test
    430 24AB,CANA
    446 72AC A NA
    XM27 120ADACNA
    29Cr-4Mo 120NAEAC NA
    29Cr-4Mo-2Ni 120NAAC NA
    446 96ACANA
    XM27 120ADACNA
    XM33 120ADAC NA
    2633120ADAC NA
    29-4C 120ADAC NA
    29Cr-4Mo 120NAAC NA
    29Cr-4Mo-2Ni 120NAAC NA
    430 24NANAno fissures
    434 24 NA NA no fissures
    436 24 NA NA no fissures
    439 24 NA NA no fissures
    18Cr-2Mo 24 NANA 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

    UNS Designation Alloy Practice(s)
    430A X, Z
    434A Z
    436A Z
    XM8 Z
    18Cr-2Mo W, Z
    446A X, Y
    XM33 W, Y
    XM27 W, X, Y
    2633 Y
    29Cr-4Mo X, Y
    29-4C Y
    29Cr-4Mo-2NI X, Y

    A 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.

    2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.

    ASTM Standards

    A370 Test Methods and Definitions for Mechanical Testing of Steel Products

    UNSPSC Code

    UNSPSC Code 11171600(Stainless steel alloys )

    DOI: 10.1520/A0763-93R09

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