ASTM A763 – Standard Practices for Detecting Susceptibility to Intergranular Attack in Ferritic Stainless Steels
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.
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 – 10).
1.1.2 Practice X—Ferric sulfate-sulfuric acid test for detecting 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 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.