Реферат

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.

Область применения

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
4390.025NAA^ANA 18Cr-2Mo0.025NAA^ANA XM270.025NAA^ANA XM330.025NAA^ANA 26-3-30.025NAA^ANA PRACTICE X—FERRIC SULFATE - SULFURIC ACID TEST
430 24A^B,CANA 446 72A^C A NA XM27 120A^DA^CNA 29Cr-4Mo 120NA^EA^C NA 29Cr-4Mo-2Ni 120NAA^C NA PRACTICE Y—COPPER-COPPER SULFATE - 50% SULFURIC ACID TEST
446 96A^CANA XM27 120A^DA^CNA XM33 120A^DA^C NA 26–3–3120A^DA^C NA 29-4C 120A^DA^C NA 29Cr-4Mo 120NAA^C NA 29Cr-4Mo-2Ni 120NAA^C NA PRACTICE Z—COPPER-COPPER SULFATE - 16% SULFURIC ACID TEST
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) S43000
430^A X, Z
S43400
434^A Z
S43600
436^A Z
S43035
XM8 Z
S44400
18Cr-2Mo W, Z
S44600
446^A X, Y
S44626
XM33 W, Y
S44627
XM27 W, X, Y
S44660
26–3–3 Y
S44700
29Cr-4Mo X, Y
S44735
29-4C Y
S44800
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.